Scientific Forecaster Discussion
fxus61 klwx 230135
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
835 PM EST Mon Jan 22 2018
a cold front will cross the area on Tuesday. High
pressure then builds over the area Tuesday night through Friday
morning then shifts offshore this weekend as another frontal
system approaches from the west.
Near term /through Tuesday/...
low pressure (both at the surface and aloft) will track into
the Great Lakes tonight and the cold front associated with the
low will pass through the Ohio Valley. A southerly flow ahead of
the boundary will strengthen overnight...and this will allow
for more mild conditions along with deeper moisture from the
Gulf of Mexico. A strengthening low-level jet ahead of the cold
front along with the deep moisture will cause showers to
increase in coverage...especially after midnight.
Models are showing strong forcing (200-meter/12 hr height
falls) over the area with pwats rising to around to 1.5 inches
or 250 to 400% of normal. In addition, wind fields will also
strengthen with models showing 850 mb and 500 mb winds of 50kt
and 80 kt respectively. With the substantial increase in winds
and moisture, there will be potential for T-storms Tue morning
through midday (12z-18z time frame). Stability indices and the
shrb (high shear/Low Cape parameter) suggest potential for
severe T-storms given up to 500 j/kg of cape and strong wind
fields just above the surface with a line of showers
accompanying sfc cdfnt. Biggest threat for severe T-storms is
east of the U.S. Route 15 corridor. Cdfnt will push east of the
ches Bay by 18z with showers ending, but over the Appalachians
the showers will continue and turn into snow showers.
A downsloping flow and increasing sunshine may offset cold
advection for a period Tuesday afternoon. Temps in the 50s and
60s are most likely.
Short term /Tuesday night through Wednesday night/...
turning colder Tue night under cold air advection pattern. Snow showers will
continue over the mtns with a few inches of accumulation
possible. A northwest flow ahead of approaching high pressure
will allow for dry conditions east of the Allegheny Highlands
along with seasonably chilly temps.
Long term /Thursday through Monday/...
dry conditions with near normal temperatures are expected for
Thursday and Friday as high pressure moves south or near our
area. Flow will change from northerly to southerly as the high
pressure moves offshore on Friday. Warm air advection will allow
temperatures to become above normal, especially for Saturday -
maybe Sunday- with some areas reaching the 50s.
Guidance suggests that a cold front will move through sometime late
Saturday or Sunday. Timing of the frontal passage and amount of quantitative precipitation forecast
is still uncertain but trending more into a Sunday event. Showers
associated to this could begin Saturday night. Behind the front, dry
conditions and cooler temperatures expected, with temperatures
dropping to near normal.
Aviation /01z Tuesday through Saturday/...
developing IFR conditions mainly 06z-15z Tue with showers with
a slight chance of thunderstorms and rain. Low level wind shear also a possibility 06-15z. Cdfnt
pushes east of terminals after 15z with winds shifting and
VFR conditions expected between Thursday and Saturday with high
pressure moving south or near our area.
winds will strengthen tonight into Tue morning with
Small Craft Advisory conditions. Showers or T-storms Tue morning may be capable
of producing brief strong convective gusts in excess of 33 kt
which may require smws. Small Craft Advisory conditions will likely persist
Wind gusts could reach Small Craft Advisory criteria on
Thursday before decreasing into Friday. Breezy conditions return
on Saturday with the cold front.
a southerly wind will strengthen tonight into Saturday morning.
Tidal anomalies will increase...but astronomical norms are low
due to the lunar phase. Therefore...minor flooding is not
expected but it will be close for sensitive areas Tuesday
morning. An offshore flow will develop Tuesday afternoon behind
a cold front.
District of Columbia...none.
Marine...Small Craft Advisory from 1 am Tuesday to midnight EST Tuesday
night for anz530>532-535-536-538>541.
Small Craft Advisory until midnight EST Tuesday night for