name: bart vd hurk
date: 2003-05-22 04:07 UTC
A warm front is overlying Zeeland (NW-SE) and steadily
(20kts) moving eastward, bringing moist air and light
precipitation. Associated cloud mass is Sc/St, currently
with cloud base around 1500ft in De Bilt but rapidly
decreasing to below 500 ft. Freezing level increases from
5000 to appr 9000ft after the front, cloud top is about
15000ft. Wind is light (20kts at 850hPa) and west. A cold
front is lying W of Ireland, and depending on travel speed
and isobaric waves will reach the West coast around midnight
or early tomorrow morning. Cold air and convective cloud
types can be anticipated for tomorrow, but timing is
uncertain.
name: Daan Vogelezang
date: 2003-05-21 06:50 UTC
WSW flow with scattered showers. Tops of Cb at 8000 ft,
base at 2000 ft. Winds are from 240 10kt at surface, 20kts
up to 10000 ft. Two cloud layers: Lower layer (Cu/Sc) with
base at 2000 ft, second layer (Sc) with base at 6000 ft and
top at 8000-8500 ft. Top temperature about -8 Celsius.
Freezing level 5000 ft rising to 5500 ft. Cloud cover for lowest
layer 6-7 okta. High layer 5-7 okta (more uncertain).
From the southwest Cirrus approaches the Netherlands,
expected at De Bilt around 9-10 UTC.
Tomorrow: The mentioned cirrus is associated with a warm
front. This front lays over the country tomorrow. Steady rainy
conditions expected.
name: Daan Vogelezang
date: 2003-05-20 06:47 UTC
Strong WSW flow. Wind speeds from 15 kts over land to 20kts
near the coast. Scattered showers over land heading NE.
Cloud base at 2500 ft, tops in Cb extending up to 8000-9000
ft. The level of the tops increases during the morning up to
12000 ft. Cloud cover 3-5 okta. Freezing level 4500 ft
decreasing to 4000 ft. Strong wind up to 35 kts at 10000 ft.
An occlusion/trough approaches the Netherlands, entering
west coast at 10 UTC. More severe convection expected on
the front, thunderstorms possible.
Tonight: The occlusion moves NE towards Denmark. Behind it
at the moment Cu/Sc fields. However, development highly
uncertain as it passes over orography (British Islands).
Tomorrow: conditions improve. Less wind, less unstable. Wind
still from SW directions. From SW Cirrus associated with the
polar jet will come in.
name: Fred Bosveld
date: 2003-05-19 09:30 UTC
The Cirrus may disappear around 13 UTC. At that stage there
will probably still be multi-layer clouds. At the end of the
afternoon clearings with cumulus will appear with tops to
20000ft possibly with thunder. The difference in development
over the North Sea and over land is small due to the
dynamical forcing.
name: Fred Bosveld
date: 2003-05-19 05:24 UTC
A low pressure system is almost stationaire NW of the british
Islands. In a SW-flow maritieme polair air is transported over
the Netherlands. A waveform coldfront passes South of the
Netherlands from SW to NE, at 12 UTC central Germany.
(HIRLAM gives a 3 hour later timing). Behind the wave a
through gives rise to increased instability. Clouds first Cu with
cloudbase 1500-2000ft, in the morning from the SW
SC/AC/NS above 3000ft. Maximum temperature 15 oC,
freezing level 5500ft, Wind SSW 6-12kn at the surface to 30-
35kn at 10000ft. Rain starting at 8 UTC in the SW of the
Netherlands and leaving the NE of the country at 14 UTC.In
the afternoon a Cirrus will disappear and cumulus develope
with cloud tops between 12000 and 16000 ft. possibly with
tunderstorm
Tomorrow: Unstable weather but timing of fronts quite
uncertain.
name: Fred Bosveld
date: 2003-05-18 10:03 UTC
A low pressure system NW of the British Islands gives a SW-
flow over the Netherlands with in it frontal systems. Last
night a front with rain passed the Netherlands with behind it
unstable polar air. Broken Cu with cloudbase 1500ft and tops
2500 ft. At 8 UTC a broken SC field with cloudbase at 8000 ft
enters Rotterdam also a small band of Cirrus is passing. SW
wind with speeds at the surface 17 kn and 30 kn at 10000ft.
Maximum temperature 17 oC. Freezing level 5500ft. Cloud
tops may upto 10000ft, more pronounced in the East of the
Netherlands with occasionally showers. In the afternoon
Cirrus will increase while cloud conditions at lower levels
staying the same.
Tomorrow: A complex front will pass but timing and activity is
still highly uncertain.
name: Fred Bosveld
date: 2003-05-17 06:53 UTC
A low pressure system NW of the British Islands gives rise to
a coming and going of fronts from the SW. This morning a
weak occlusion front passes over the Netherlands from SW to
NE with light rain, cloudbase height 4000ft. After this front
from 10 UTC onward unstable air comes in with isolated
showers evolving during the day. All cloudtops above 10000ft
with maximum values up to 16000ft. Freezing level at 6500ft.
Wind speed 6-10kn at the surface, 15 to 20 kn upto 10000ft
with gusts close to showers up to 25-30 kn. Winddirection
SSW. Maximum surface temperature 16oC.
Tomorrow: Tonight the next occlusion front will pass the
Netherlands with behind it unstable polar air.
name: Fred Bosveld
date: 2003-05-16 07:03 UTC
A weak high pressure sytem NE of the Netherlands gives a
weak SE flow at the surface (<10kn). Wind veers with height
but still weak up to 18000ft. A frontal system over England
moves slowly to the North East. Cirrus clouds from this front
are progressing already over the Netherlands, in the later
afternoon mid level clouds will enter the Netherlands. From
10:00Z Cu will develop with cloud base height at 4000ft and
tops to 8000 ft, cloud tops drying due to dry air mixing aloft.
Freezing level at 4400ft. Cu development will be somewhat
more pronounced in the East, 3 octa.
Tomorrow: The frontal system will lay over the Netherlands
giving high, mid-level clouds and rain.
name: Daan Vogelezang
date: 2003-05-15 06:43 UTC
Situation: weak northwesterly flow with slightly unstable air.
Scattered showers more in the north than in the south of the
country. Winds are weak (10 kts) from 280-300 deg. A ridge
of high pressure passes the country in the afternoon. Behind
it, the winds go to W/SW directions, decreasing to about 5
kts. Cloud regime is locally determined (weak) convective with
cloud base at 2000-2500 ft. Freezing level at 3000-3500 ft.
Cloud cover over land may increase from 1-3 okta in the
morning to about 5-6 okta in the afternoon. Cloud tops at
different altitudes, but may extend to 10000 ft or somewhat
higher. Some scattered/broken Ac/Sc with base between
4000-8000 ft present.
Tomorrow: a frontal system approaches from SW. Cu/Sc
ahead of it at 2000 ft. Upon the approach, midlevel and
highlevel clouds (Ac/Ci) cover increase from SW.
name: Daan Vogelezang
date: 2003-05-14 06:48 UTC
situation: Cold polar unstable air with several scattered but
sometimes organised showers over the whole country. With a
West Northwesterly flow two frontal systems approach from
over the North sea. Strong convection associated with the
fronts will pass The Netherlands. By 18 UTC both systems
have left by the east border.
Most active Cb expected in the North of the country.
Winds are from 250-270 15 kts, not much changing with
height. But gusts up to 35 kts possible in Cb.
At the same time from England (East Anglia) a large
Cumulus/Stratocumulus field approaches the country. about
7/8 octa cover, little or no rain reported on it, cloud base at
about 4000-5000 ft (east edge), decreasing to about 3000 ft.
more west. Freezing level is around 3000 ft. Radiation
temperature at the cloudtop about -11 Celsius (8000-9000
ft). The edge of the Cu/Sc-field is due to reach the Cabauw
area around 9 UTC.
For thursday and friday the atmosphere calms down due to
the increasing influence of a high pressure system above the
Atlantic. Cloud conditions will develop into more Cu/Sc with
subsidence inversion aloft.
name: Bart van den Hurk
date: 2003-05-13 04:07 UTC
A steady westerly flow originating from a depression W of
Scotland brings cold polar air to the Netherlands, following
a frontal system with precipitation that passed last night.
Dewpoint of the air mass being advected is decreasing, but
absolute temperature in the upper air is decreasing as well.
Birmingham radiosonde of 00Z is 5K cooler in the upper air
than De Bilt, implying a strong increase of instability. At
present, air over the Northsea is moving a bit anti-cyclonic
which probably inhibits cumulus formation due to subsidence,
but over land cumulus formation may easily develop when
temperature exceeds appr. 11C (from about 9 UTC onwards),
and once formed (cloud base 1200ft) a quick development to
deep Cb occurs (top > 25000ft) with heavy showers and wind
gusts. The flow is associated with small waves in the
isobares that will give rise to spatial organisation of
these showers into streets. Winds are WNW, about 20kts at
850hPa.
For tomorrow a similar picture emerges: the depression stays
at the same location, cold unstable air with heavy showers
will be advected.
name: Rob van Dorland
date: 2003-05-12 07:45 UTC
A low pressure area (surface and upper air) in the vicinity of
Scotland is travelling in south east direction and propagates
cold polar air to Europe. An associated trough over the UK is
moving eastward and is expected to reach the north coast in
the evening. An occlusion front is positioned between the UK
and France and moving faster than expected towards the
north east. Cirrus associating with this zone is expected to
arrive between 9 an 10 UTC in the middle of the country. Sc
and Cu Cloud base is estimated 1500-2000 ft and lifting uptil
2500 ft. Cloud tops are at 8000 ft. In the afternoon some
showers are possible.
Wind is 15 kts near the ground and increasing with height (25
kts at 3000 ft). During showers ground winds may show 30 to
35 kts.
name: Rob van Dorland
date: 2003-05-11 08:37 UTC
A stationary low pressure system is found in the vicinity of
Iceland. In the polar air troughs from the Gulf of Biskai are
moving in the SW upper air flow towards the Northsea. A
weak front is touching the coastline in the morning, giving
some precipitation in the north west. A more active
precipitation area is present over the coast line of Belgium,
travelling to the north east (at 10.00 UTC in Rotterdam).
According to the temp (De Bilt, 00 UTC and Hirllam, 12 UTC)
cumuli may occur from 9 to 10 UTC onwards with cloud base
at 2000 to 3000 ft. Due to the much drier air than yesterday
cloud cover will be less 2-3 octa, but less near the coast.
Cloud tops are estimated at 6000 ft in the early afternoon.
Behind the cold front cloud tops may grow to 18000 ft later in
the afternoon. Then cloud cover may also increase to 4-6
octa. Large cirrus fields are moving into the south of the
Netherlands. At 12 to 13 UTC the edge will be situated over
De Bilt. Wind: S-SE 5 kts at the ground and 15 to 20 kts
Outlook: A frontal system is slowly approaching from the
south west. This causes some rain in the evening. Tomorrow
the Iselandic low is travelling in the direction of the North
sea, resulting in increasing probabilities of rainy days.
name: Rob van Dorland
date: 2003-05-10 07:56 UTC
Behind the cold front, which passed slowly yesterday, colder
polar air has reached the Netherlands. A weak trough is
passing over. At 12 UTC it will be found over the east of the
country. Behind this trough a modest idge of high pressure is
building up. The day started with some high clouds at 6000 to
7000 ft, associated with the passing trough. Today,
convection is expected when the temperature rises above the
14 to 15 degrees. This will be the case between 9 and 10
UTC. The CCL is situated at about 2000 ft at the coast to
3000 ft inland. The cloud tops in the early afternoon are at
6000 to 7000 ft. Above this level we have a critical unstable
profile, implying the possibility of showers later in the
afternoon and if they occur mainly in the east of the
Netherlands. Cloud cover will be around 4 to 5 octa, perhaps
somewhat more in the east. Wind is west (5-10 kts at ground
level) and W to SW (15 kts at cloud levels).
Southwest of the UK a L pressure system is developing, which
might give some cirrus clouds. The outlook for tomorrow is the
passing over of the associated but weak front. This might
cause multi layer clouds.
name: Rob van Dorland
date: 2003-05-09 06:53 UTC
A cold front is oriented SSW-NNE, propagating slower than
expected with small amounts of precipitation. The delay of
this frontal zone has been caused by the northward moving
active warmfront at the 8th of may. This system induced the
built up of a modest high pressure ridge at its westside,
hence the delay. Winds are weak and are expected to stay
weak in the afternoon at ground level. Behind the passing
cold front, ground winds will be north changing to west later
in the afternoon. Behind the cold front clear sky polar air is
reaching the Dutch coastline.
Later in the afternoon, from 1:00 UT these sunny spells are
expected in the NW part of the Netherlands. Small cumuli are
expected to develope ove land. Cloud base at 2500 ft and
tops at 5000 ft, whicht is about the freezing level. Cloud
cover is estimated 2 octa. Also, there may be some Cirrus at
600 hPa.
Tomorrow we will dryer conditions. A low pressure system is
appraoching from de south west, probably giving high
cloudiness.
name: Erik van Meijgaard
date: 2003-05-08 06:24 UTC
Situation and Forecast for Thursday May 8th
A rather inactive cold front is approaching from Britain and is
expected to cross the Netherlands the coming night. High
clouds associated with the front are currently over the North
Sea touching North Holland but have a tendency to move NE.
A warm front regenerated from an earlier frontal zone over
Central Europe is moving NNE across France. Scattered thin
cirrus associated with this front is already over the south
east of the Netherlands. In the second part of the day thicker
cirrus and later on altocumulus/stratus will spread over the
central part of the country. There is the possibility of a late
afternoon shower in the southeast. There will be no boundary-
layer cloud development today owing to the very dry
conditions of the lower troposphere. Early morning fog
(somewhat thicker than yesterday) will have disappeared
before 10 local time. The wind is weak, variable at first, west
later.
Outlook for Friday May 9th
After the corssing of the inactive coldfront (scattered
showers are possible) cool and unstable maritime air will come
in during the moring hours. Development of broken cumulus in
day-time is expected. It is not clear yet whether there will
still be cirrus trailing the cold front.
name: Erik van Meijgaard
date: 2003-05-07 06:39 UTC
Situation and Forecast for Wednesday May 7th
A narrow ridge of high pressure oriented WSW-ENE is situated
over the Netherlands. Winds are weak. Cirrus fields with
occasional altocumulus associated with a frontal system over
Britain moved in after midnight. The cirrus is not expected to
dissipate or dissolve in the coming hours since the flow at 300
hPa is not anti-cyclonal. Boundary-layer clouds are not
expected to develop as the boundary layer is toodry and
large-scale subsidence in the lower troposphere is significant.
If cumulus develops, they will be very shallow with cloud base
at 1200 m and cloud cover will not exceed 2 octas. Patches
of ground fog which appeared late night have all disappeared.
Outlook for Thursday May 8th
A cold front over Britain is slowly moving ESE-ward. At the
same time a warm front over France is moving NNW-ward. In
the second part of the day the warmt front will affect
conditions in the Netherlands with convective showers
embedded in a frontal zone. The cold front will cross in the
night from Thursday to Friday
name: Erik van Meijgaard
date: 2003-05-06 06:39 UTC
Situation and forecast for Tuesday May 6th
Frontal zone at 06:00 UTC very slowly moving to the ENE with
a tendency to dissolve. Cirrus shields associated with the
front are as far west as the central North Sea and East
England. In the coarse of the day a westerly flow related to
the building up of a ridge of high pressure from the Azores will
bring cool and drier maritime air. Over the North Sea (very)
few broken cumulus (not more than 2 octas) is present due to
advection. Over land cumulus will arise due to increasing
radiation but not earlier than mid and high level clouds have
been sufficiently dissolved. This is expected to occur around
12:00 local time (max 4 octas). Cloud base over land starts at
800-1000 meter and is gradually lifted to 1500 meter, the
vertical extension is expected to be not more than 300 meter.
Mid-level clouds will eventually disappear, but it is uncertain
whether this happens with high-level clouds as well.
Outlook for Wednesday May 7th
A ridge of high pressure with a separate center lies over the
north of the country giving rise to a NE-flow in the boundary
layer. Model cloud prediction suggests it will be entirely cloud
free in the first part of the day. Cumulus humilis is expected
to emerge at 10:00 local time, and there is a chance of fog in
the early morning,
name: Bart van den Hurk
date: 2003-05-05 04:56 UTC
As expected, a frontal system (oriented ssw-nne) is slowly
moving eastwards, associated with considerable precipitation
and unstable air (cloud base appr 10000 ft). This system
will pass the westcoast in the morning, slowly moving
eastwards by the end of the day. In the east-sector, air is
fairly unstable, but low-air inversions may be prohibited by
cold air advection from sw. This implies possible showers in
this eastern part of the country (clouds topping at around
15000ft) but shower activity is more likely further to the
east across the border in Germany, where this sw cold air
advection is less dominant and radiative heating may trigger
the convection.
For tuesday 6 May the frontal system is east of the
Netherlands, but waves in the system may bring precipitation
showers westward into the Netherlands. The weat of the
Netherlands is gaining influence from a high pressure ridge,
giving rise to cloud and light precipitation mainly in the
Northern part of the country. High clouds will likely be
present in the West as well.
name: Erik van Meijgaard
date: 2003-05-04 12:47 UTC
(Forecast issued at meteo briefing Sunday May 4th, 06 UTC.)
Moderate southerly flow of warm and gradually drier air
gives rise to sunny and warm conditions. Trajectories in
boundary layer are from S to SSE, in the upper air between
SSW and WSW. No boundary-layer clouds and mid-level clouds
in daytime. Abundant cirrus present in the morning hours
with a tendency to get thinner in the coarse of the day.
However, given the relatively mosit upper-air temp it is
unlikely that the cirrus fields will entirely dissolve.
Outlook for Monday May 5th: frontal zone between Ireland and
Biscay will move eastward and activate due to cyclogenesis
over Western France. Conditions will be unstable with
considrable chances of showers or showery rain during
daytime, most likely past noon. In the eastern part of the
country the day might start sunny and the temperature will
quickly rise resulting in pre-frontal showers
name: bart vd hurk
date: 2003-05-03 06:38 UTC
For saturday 3 May the situation seems to be pretty clear-sky, with possibly very little mid-level clouds.
Winds are 40-45 kts (1000-3000ft) in the morning, decreasing by 5-10 kts in the afternoon.
For sunday a bright cloud-free day with southerly flow is expected.
Monday 5 May a frontal system is passing over with a Low-distortion (?) travelling Northward, probably giving rain and dense cloud cover during daytime.