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FXUS61 KLWX 260809

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
409 AM EDT Tue Sep 26 2017

High pressure will slowly weaken its grip over the area today 
and Wednesday as Hurricane Maria stalls in the western 
Atlantic. A cold front will move through Thursday, bringing 
seasonable temperatures from late this week through early next 
week. The front will also push Hurricane Maria out to sea. 
Little if any rain is expected through early next week.


Maria is hanging off the NC coast this morning, but the wind
field has expanded enough such that an easterly flow is
strenghtening over our region. Some low clouds are trying to
move into the region from the ocean. Further west, we have
patchy fog in the more interior areas. High pressure to our
north is weaker today, and with the stronger easterly flow, 
temperatures today should be a little cooler than yesterday,
though we do expect most of the clouds and fog to burn off.
Highs mainly 80s. A few showers could reach southern MD, but
most likely they stay southeast.

Tonight, Maria will remain off the NC coast. A few showers may
reach southern MD, but again, odds are not high. We could see
more clouds advect in as well from the east, while inland could
see more patchy fog. All in all, not much different from what
we've seen lately. Lows mainly in the 60s.


Maria will start turning east away from the region late 
Wednesday, so we will still see some clouds especially in 
eastern areas from it on Wednesday, and perhaps a stray shower 
in southern MD. Otherwise, we likely end up a bit warmer 
Wednesday as clouds should overall be reduced as the storm
begins turning out to sea. Highs mainly 80s, but a few degrees 
above today.

Strong cold front moves in early Thursday, with a pretty strong
breeze expected. However, with limited moisture and dynamics,
don't expect any showers with the front at this time. Humidity
will lower and highs may actually fail to reach 80 for the first
time in quite a few days. Skies will turn out mostly sunny.
Significantly cooler with diminishing wind Thursday night, with
40s and low 50s common.


Overnight model guidance appears to have continued its trend of
a quicker/weaker upper trough crossing the region Friday night 
into Saturday. This appears to be in response to a stronger 
upper low moving into western NOAM which shoves everything 
downstream eastward quicker. The trough axis/surface reflection 
in the form of a reinforcing cold front are now progged to pass 
through our area during the overnight hours. This decreases 
further the chance for appreciable rainfall. Behind the front, 
an autumnal high of Canadian origins (~1030 mb) builds north of 
the area bringing cooler and drier air through the weekend.

The tendency of lower heights over the western CONUS would tend
to support a stronger ridge developing over the middle portion 
of the country. This ridge then builds towards the eastern CONUS
during the first part of next week. This results in a very low 
chance of rain.
In fact, the last several runs of the GEFS have shown a very 
strong negative PNA during this time which would suggest strong 
to extreme ridging building over the eastern CONUS in the 
extended. Operational ECMWF not as extreme but its ensembles 
agree with the idea of a strongly negative PNA pattern early 
next week. By extrapolation, this could lead to significantly 
warmer than normal temperatures by the middle of next week. 
However, the position of the (~1040 mb) surface high over 
southeastern Canada could keep a cooler wedge of air near the 
surface offsetting the anomalously high heights aloft through at
least Tuesday.


With easterly flow off the ocean developing north of Maria, some
low clouds have been trying to advect into the region from the
ocean. So far they have not reached our terminals, but concern
remains that they will before or right around sunrise, so have
maintained IFR for a time this morning at BWI/DCA/IAD. Further
west, low clouds should not reach MRB and CHO, but patchy fog
may reduce vis. After sunrise, low clouds should gradually lift
and fog should burn off, resulting in VFR conditions for the
balance of the day. Another round of low clouds and fog is
possible tonight, with a return to VFR likely again on Wednesday
afternoon. By Thursday, a strong cold front will bring gusty
northwest winds, preventing any more IFR or even MVFR
conditions, even in the morning. No more than a very isolated
shower is expected through the next few days.

Mainly VFR Fri-Sat. N winds 10 kts, a few gusts Sat.


SCA over middle bay and adjancent waterways through Wednesday
with Maria hanging off the coast. Then, strong cold front will
likely bring SCA to all waters Thursday, and potential for gales
remains with this front. Winds start diminishing late Thursday.

Northerly surge in cool/dry advection early Saturday will 
likely lead to a period of SCA conditions.


Water levels will remain elevated through midweek before a cold
frontal passage turns winds northerly and pushes excess water 
out the mouth of the Bay on Thursday.


MD...Coastal Flood Advisory until noon EDT today for MDZ017.
MARINE...Small Craft Advisory from midnight tonight to 6 PM EDT 
     Wednesday for ANZ533-541-542.
     Small Craft Advisory until 6 PM EDT Wednesday for ANZ534-537-



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