Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Raleigh NC
335 PM EST Monday Nov 30 2015
Synopsis...high pressure will ridge south through the Carolinas...
resulting in cool and wet conditions through Tuesday. A cold front
will sweep across the area on Wednesday.
Near term /through tonight/...
as of 330 PM Monday...
A surface cold front has now pushed all the way into SC and cad has
taken over central NC. Patchy rain..mostly light...continues to
move west to east across the area amidst weak isentropic lift and a
few very subtle disturbances topping the broad ridge aloft. Near
term guidance shows a large spread in where the "heavier" areas of
rain will be this afternoon and evening...but with time rain should
become focused over the northwest Piedmont in response to
strengthening upper level diffluence and low-level isentropic upglide
associated with an upper jet merging from the base of the Central
Plains upper low. Expect generally a quarter to half inch in the
northwest Piedmont and lesser amounts to the southeast.
Otherwise...temperatures will hold steady this afternoon and then fall a
little overnight into the 40s areawide.
Short term /Tuesday and Tuesday night/...
as of 330 PM Monday...
A Stout shortwave diving into the back of the Central Plains upper
low will send a pair of merging frontal zones over the MS River
Valley/deep south our way on Tuesday. Meanwhile...the cad front to our south will lift
back north as a warm front...but GFS/NAM bufr soundings support the
notion that the cad airmass will hold and only slowly erode during
the day. Deep moisture will shift north and a period weak forcing
ahead of the approaching the upper trough will lead to only isolated
showers. Highs in the northwest Piedmont may reach 50...while
in the southeast temperatures should approach the middle 60s.
The cold front will move into the mountains Tuesday night and then
sweep across central NC on Wednesday. Southeasterly flow ahead of
the front...combined with the arrival of stronger height falls aloft
will cause precipitation to increase in coverage and intensity over western
NC. Guidance have trended a little heavier and and further east
with the axis of heaviest quantitative precipitation forecast...ranging from 0.75" to 1" in the
northwest Piedmont through 12z Wednesday. The GFS shows upwards of
1.5 to 2 inches through midday Wednesday. The gradient in quantitative precipitation forecast is
large across the western Piedmont and the heaviest quantitative precipitation forecast is more into
the foothills. Given rainfall amounts around an inch earlier
today...and some additional rainfall tonight...a Flash Flood Watch
isn't out of the question for Tuesday night and early
Wednesday...but it seems prudent to first see how much rain falls
Temperatures will slowly rise Tuesday through the 50s Tuesday night as a
southerly wind begins to develop...which should help to disperse and
fog that may develop early in the night.
Long term /Wednesday through Sunday/...
as of 316 am Monday...
Wednesday and Wednesday night: closed upper low will progress
eastward through the Great Lakes Wednesday-Wednesday. Models have
trended slower with the timing of the attendant cold front into the
area on Wednesday...now indicating late Wednesday afternoon/evening.
The approach of the upper trough and increasing upper divergence in
the right entrance region of a 140-150kt jet when combined with
frontal forcing should support high chance to likely probability of precipitation chances
across the area. Latest sref plume/spaghetti plots suggest
instability will remain limited with no mention of thunder planned
at this time.
Slower arrival of front eastward into the area could mean that
eastern portions of the forecast area could stay mostly dry until
late in the day...which should translate into warmer daytime highs.
Highs ranging from lower northwest to Lower/Middle 70s southeast.
Rain chances should diminish from west to east after midnight Post-
frontal cold air advection governing min temperatures. Lows ranging from upper 30s/near
40northwest to upper 40s/near 50 southeast.
Thursday through sunday: closed upper low will continue to move
eastward filling along the way as it finally exits the New England
coast Thursday night/early Friday. In its wake...chaotic split flow
regime may allow a compact/weak upper low to develop across the area
by the weekend as numerous individual shortwaves conglomerate over
the region. Medium-range model solutions agree that any surface
development and associated rain chances will remain east and
offshore with a strengthening ~1040mb surface high dominating a dry
weather pattern across the Carolinas.
Expect slightly below normal temperatures to close the work week
with temperatures moderating to normal by Sunday/early next week.
Aviation /18z Monday through Sunday/...
as of 100 PM Monday...
Cold air damming is well entrenched over the area and poor aviation
conditions to continue through the taf period. Periods of light rain
and drizzle will also continue...with some slightly heavier rain
possible this evening and early tonight...primarily from kgso/kint to
krdu and north. IFR ceilings will certainly continue...and LIFR
conditions are possible with ceilings potentially dropping to around
200ft at least temporarily. Winds will remain light and out of the
northeast. If there is any improvement on Tuesday it will be at
kfay and/or krwi during the afternoon hours...as the cold air
damming is not likely to erode very fast.
Outlook...IFR/LIFR conditions will briefly improve on Tuesday...but
fog is expected to develop Tuesday night. Gusty southwest winds will
precede a cold front set to sweep across the area on Wednesday and
usher in a return to VFR conditions into the weekend.