Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Pittsburgh PA
952 PM EST Monday Dec 22 2014
low pressure in the midwestern states will bring warmer
temperatures and rain to the region Tuesday night and Wednesday.
Gusty winds will accompany the passage of a cold front on
Near term /through Tuesday/...
10pm update...have extended the advisory in Garrett until 09z.
Temperatures refuse to rise there and freezing drizzle is likely on
going. Have modified temperatures and probability of precipitation overnight using latest hires
Freezing rain rain advisory will remain in effect for the ridge zones of Maryland and
WV this evening as light precipitation continues to be augmented by subfreezing surface temperatures.
Otherwise...expect cloud cover to gradually refill in warm...moist
advection on the eastern flank of midwrn low pressure. That process will retard
the diurnal temperature trend and lows about 5 to 10 degrees above the
avgs were forecast using bias corrected MOS.
Most of the model guidance suggests that Tuesday will remain a
relatively benign day as a shortwave digging the upper trough
strengthens the southerly flow and warm advection over the region.
Expect temperatures to be close to 15 degrees above seasonal
values. The bulk of the precipitation does not look to push into the
region until later in the period...so chance probability of precipitation were maintained
during the day Tuesday.
Short term /Tuesday night through Thursday/...
sharply-amplified upper trough over the midwrn states will lift into
the Great Lakes region Tuesday night through Wednesday. Ahead of this wave...strong warm
and moist southerly flow will be maintained...providing opportunity for
widespread rain and increasing warmth. Temperatures on Wednesday have a good likelihood
of reaching at least lower 60s...limited primarily by cloud cover and precipitation.
It appears rain may occur in two waves. First wave will develop Tuesday
night into Wednesday morning as warm air advection increases considerably ahead of
aprchg upper wave. Second wave may occur later Wednesday afternoon as pre-
frontal surface trough moves across warm sector. As a result...two
relative maxima in probability of precipitation were introduced during Tuesday night-Wednesday night period.
Prior to passage of cold front early Thursday morning...region will be located in
dry slot of upper system. Local research suggests this pattern may
be favorable for strong wind concerns Wednesday night in all areas and
especially Thursday in the higher terrain. This threat was included in the
hazardous weather outlook.
Cold front will cross the region early Thursday morning. Maxima likely will be
reached early in the day...with cold air advection dominating during
the day. Chances for snow showers will increase with passage of cold pool
aloft as instability increases amid steep low-level lapse rates. Fetch will
not be favorable for lake enhancements except perhaps in far northern
zones...so no significant accums expected. Snow showers may continue in higher
terrain of PA/MD/WV into Thursday evening but will wane quickly as
inversion heights lower.
Long term /Thursday night through Monday/...
minimal changes were made to the extended as latest guidance
showed both poor agreement and continuity...and any changes that
were made were primarily based on ensemble means. With that...dry
conditions and temperatures approximately 10 degrees above normal
are forecast on Friday as ridging transitions over the region. A
trough of low pressure will then result in unsettled conditions
Saturday and Sunday.
Aviation /03z Tuesday through Saturday/...
VFR can be expected through much of the night...with deterioration to
MVFR thereafter as warm front surges northward. As that feature
progresses...low end VFR should rtn until rain and restriction chances
increases on Tuesday night.
Outlook.../Tuesday night through Saturday/...
the systems cold front will continue restriction potential into Thursday.
Maryland...Freezing Rain Advisory until 4 am EST Tuesday for mdz001.