699 
fxus61 kctp 201941 
afdctp 


Area forecast discussion 
National Weather Service State College PA 
341 PM EDT Sat Mar 20 2010 


Synopsis... 
unseasonably mild and mainly dry conditions will continue through 
most of the day on Sunday. A storm system developing over the 
lower Mississippi Valley will move slowly northeast into the middle 
Atlantic by Tuesday. This system will be accompanied by a period 
of wet weather to start the work week. 


&& 


Near term /until 6 am Sunday morning/... 
another very mild day in progress across the commonwealth. Pre- 
frontal trough associated with weak cold front crossing the lower 
Great Lakes is producing streets of cumulus over the northwest 
mountains. Forecast soundings show a deeply mixed boundary layer up 
to around 800 mb late this afternoon and have mixed down maximum T from this 
level. The deep mixing has also allowed for occasional wind gusts up to 
20kts. Not much else to say with temperatures averaging about 20 
degrees above middle-late March climatology...not bad for the first day of 
Spring. 


Expect the overnight period to remain relatively quiet with just 
a few scattered showers possible in vicinity of the frontal boundary moving 
southeastward from the lower lakes into north-central PA. As low level 
moisture continues to slowly increase...could see some patchy fog 
around daybreak across portions of south-central and southeast 
PA. 


&& 


Short term /6 am Sunday morning through 6 PM Sunday/... 
strengthening middle/upper level closed circulation over the lower 
MS valley will afford an evolving/slow moving surface low across 
the Tennessee Valley during the day on Sunday. Still not much forcing to 
work with as the main northern stream jet entrance region stays 
over the St Lawrence River valley. The front over north-central PA 
should also retreat nwwd...likely ensuring one more nice day. 
Will continue to just mention schc/chance showers...but think by in 
large most areas will stay dry. An increase in cloud cover will 
cool temperatures a few degrees from todays maximums...but still well above 
normal for this time of year. 


&& 


Long term /Sunday night through Saturday/... 
guidance has continued a slower arrival of moisture into the 
middle-Atlantic region...however oper GFS continues to suggest a slug 
of precipitation sun evening across northwest mountains sliding into New York state. 


Focus turns towards cutoff low which guidance has trended further 
south into Alabama sun evening then turning NE twrds Virginia Monday night. This 
scenario introduces more uncertainty on precipitation introduction into 
central PA...or favoring after daybreak Monday. Shallow boundary layer 
inversion may hold temperatures Monday in the 50s. At this time have maintained a chance 
probability of precipitation Sun night...however could see this holding off until after 12z Monday 
for much of the County warning forecast area. Several oper solutions hinting at a dry slot 
entrained into the cutoff low Monday evening...which could further limit 
precipitation totals. Precipitable water values still prognosticated around 1.00 inch to 1.25 
across the susq-valley Monday afternoon-Tuesday morning. This coupled with 850mb 
wind diffluent wind field and exit region of atmos river suggests 
quantitative precipitation forecast totals will be highest across the susq-valley region. At this time have 
36hr precipitation totals of the aforementioned region between 0.8 to 
1... lower totals further northwest. Potential for flooding appears 
low at this time...based on preceding stretch of dry weather and steadily 
declining stream heights. 


Wednesday will feature improving weather from west to east as the shortwave departs 
the region...lingering moisture across eastern portion of County warning forecast area. 
Confidence is increasing that trough axis will quickly depart as 
well with a return to seasonal conds late next week...then possibly 
another system approaching from the west late next week. Temperatures should 
be warm enough to limit any precipitation as rain. 


&& 


Aviation /19z Saturday through Thursday/... 
VFR flying continues for the most part over the next 24 hours. 
Some lower ceilings are possible across the northwest airfields tonight as 
weak cold front slowly drops southeastward into north-central PA. As low 
level moisture continues to slowly increase ahead of the large 
storm system moving into the lower MS valley...some patchy light 
fog-haze /3-6sm/ is possible around daybreak Sunday. 


Outlook... 
sun...no sig weather expected. 
Monday...rain/IFR ceilings possible. 
Tuesday...shra/IFR ceilings possible. 
Wednesday...no sig weather expected. 


&& 


Fire weather... 
very dry conditions will continue with minimum relative humidity/S in the low to 
middle 30 percent range this afternoon. 10hr fine fuels are below 10 percent 
across all of central PA. A weak cold front/pre-frontal trough 
will cross the lower lakes and move into the northwest mountains. Occasional 
wind gusts between 20-25 miles per hour will be possible this afternoon in 
the vicinity of this front...promoted by deep low level mixing. 
Visible satellite imagery is also showing some cumulus developing 
in this area...another sign of a well-mixed/increasingly unstable 
lower atmosphere beneath a subsidence inversion. This front will 
become nearly stationary as it drifts southeast into central PA on 
Sunday...with little to no precipitation expected. Moderate...to 
perhaps heavy rainfall is anticipated Monday into Monday night as 
a slow moving storm system moves east from the Southern Plains. 


&& 


Climate... 
Spring officially began at 132 PM EDT. 


&& 


Ctp watches/warnings/advisories... 
none. 


&& 


$$ 
Synopsis...steinbugl 
near term...steinbugl 
short term...steinbugl 
long term...dangelo/beachler 
aviation...steinbugl 
fire weather...steinbugl 
climate...steinbugl