Scientific Forecaster Discussion
fxus61 klwx 200107
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
907 PM EDT Thu Apr 19 2018
an unseasonably strong area of high pressure will migrate across
the Great Lakes and into the northeastern U.S. Friday into the
weekend, then move offshore early next week as low pressure
approaches from the lower Mississippi River valley.
Near term /until 6 am Friday morning/...
as a cold front moves farther away to the southeast, the
pressure gradient is lessening and winds are diminishing
gradually. The same can be said for the stratocumulus clouds.
Moisture is decreasing rapidly enough that the chance for any
snow showers in the mountains is coming to an end as well.
A freeze warning has been issued for much of the area between
I-95 and I-81. Winds likely stay up for most areas tonight (10
knots or so), but 925 mb temperatures drop to -3 to -5 c which
should correspond to surface temperatures at or a little below
freezing at the surface. Temperature trends and model guidance
don't support any changes to the headline this evening.
Short term /6 am Friday morning through Saturday night/...
Canadian high pressure will build north of our area from the
Great Lakes on Friday. Sunny and breezy conditions are expected
with wind gusts generally in the 20 to 30 mph range. Winds will
diminish in the evening as high pressure moves closer and the
Light winds and clear to mostly clear conditions are expected Friday
night. May need to watch temperatures again for possible
freezing conditions, mainly over the Shenandoah Valley and
Pleasant but somewhat cooler than normal conditions are expected
Saturday into Saturday night as the high slowly moves by to the
north of the area.
Long term /Sunday through Thursday/...
high pressure centered over the eastern Great Lakes/northeast
will continue to dominate our weather on Sunday bringing dry
conditions and slightly below normal temperatures to the region.
By Sunday night, models have a cutoff upper-level low and associated
surface low tracking through the deep south. Deterministic models
diverge significantly with the handling of this system. The
deterministic GFS moves this system up the East Coast and into our
County Warning Area by Monday night. The gefs support the operational GFS solution,
suggesting that a period of rainfall may be possible Monday night
through Tuesday with this system. This differs significantly from
the 00z Euro, which keeps the system stalled out to our south until
Wednesday, when it is picked up by a trough approaching from the
Midwest. The 00z European ensembles showed a wide range of
solutions, suggesting that uncertainty is high with this event.
Generally speaking, Monday appears to be mostly dry and an unsettled
period of weather will be likely sometime in the Tuesday through
Wednesday period. However, exact timing and details remain up in
the air. Regardless of what happens with the upper-level cutoff,
it appears as though some precipitation will be possible on
Wednesday as an upper-level trough swings in from the Midwest.
Aviation /01z Friday through Tuesday/...
VFR through Saturday. Remain stratocumulus clouds around 5kft
should be dissipating after midnight as high pressure builds to
the north from the Great Lakes. Gusty northwest flow should remain
below 30 kt, potentially becoming 10 kt or less at times
tonight. Gusts may peak around 25 kt Friday morning before
diminishing through the afternoon, then becoming light north
VFR conditions are expected for the weekend into Monday. Sub-
VFR conditions are possible Monday night through Wednesday as
an area of low pressure approaches the region from the south.
there are still a few gale force gusts on the Bay this evening,
but observational trends and model guidance suggest the warning
will be able to be dropped for most if not all waters by
evening's end. A Small Craft Advisory follows into Friday with
northwest flow gusting 20-25 kt at times. Winds are expected to
fall below Small Craft Advisory criteria Friday night and
remain light through the weekend.
Sub Small Craft Advisory conditions are forecast to persist into early next week
as a ridge of high pressure should keep winds light.
District of Columbia...none.
Maryland...freeze warning from 2 am to 9 am EDT Friday for mdz003>006-
Virginia...freeze warning from 2 am to 9 am EDT Friday for vaz025>031-
WV...freeze warning from 2 am to 9 am EDT Friday for wvz051>053.
Marine...Small Craft Advisory until 6 PM EDT Friday for anz531>533-536-
Gale Warning until 11 PM EDT this evening for anz531>533-536-
Small Craft Advisory until 6 PM EDT Friday for anz530-535-538-
Small Craft Advisory from 6 am to 6 PM EDT Friday for anz534-
Gale Warning until 6 am EDT Friday for anz534-543.