998 
fxus61 kctp 061938 
afdctp 


Area forecast discussion 
National Weather Service State College PA 
338 PM EDT Sat Sep 6 2008 


Synopsis... 
remnants of Tropical Storm Hanna was centered near Salisbury 
Maryland this afternoon and will track to the northeast reaching 
the southern New England coast late tonight. A large area of heavy 
rain falling over the middle and lower susq valley (and points 
east) will taper off this evening. This storm will bring 
potentially flooding rains in excess of 4 inches to parts of the 
lower Susquehanna valley and east central mountains of 
Pennsylvania. Periods of lighter rain or showers will affect most 
of central and northern Pennsylvania. Gradual clearing skies will 
spread east across the commonwealth late tonight through Sunday 
morning. A return to dry conditions is expected Sunday into 
Monday...as high pressure builds eastward. A cold front from the 
plains will scattered mainly afternoon showers and thunderstorms 
to the area on Tuesday. Another period of dry and cooler weather 
will follow for Wednesday and Thursday. 


&& 


Near term /until 6 am Sunday morning/... 
deformation area of heavy rain has focused the highest quantitative precipitation forecast totals 
thus far (2.5 to 3 inches) just to the west of a kthv and kmdt 
line. Expect to see another 1...to perhaps 2 inches across the 
Flood Watch area (6 counties throughout the lower susq valley and 
NE to Schuylkill cty). These rainfall amounts will pose little 
flooding threat to most streams and creeks considering very high 
6/12 hour headwater flood guidance of 4-6 inches and precipitation 
amounts being overestimated by a factor of 2 to 3 near the 0.5 and 
1.5 degree bright band locations between about 70 and 100 nm. 


Gradual improving trend will occur later this evening through the 
overnight...with little more than scattered evening showers across 
the central and western mountains mins will settle into the upper 40s 
across the northern mountains and around 60f in the southeast. 


Flood Watch remains in effect into Sunday afternoon to account for 
longer term runoff into the larger streams...though the bulk of 
impact on the smaller streams impact will occur during the next 3 
to 5 hours. 


Northerly winds will be increasing across the lower susq valley 
late today...but most of the peak gusts may stay in the 25 to 35 knots 
range. Will allow the evening shift to deal with this secondary 
weather issue/Wind Advisory. 


&& 


Short term /6 am Sunday morning through 6 PM Sunday/... 
high pressure builds into the region Sunday bringing a good amount 
of sunshine with near normal temperatures in the 70s and comfortably 
lower humidity. 


Will continue Flood Watch (for now) into Sunday afternoon at this time...as 
rainfall takes a while to reach some of the larger tribs and 
rivers. 


&& 


Long term /Sunday night through Saturday/... 
Sun night through Monday will feature a developing trough across northern 
plains. Ensembles have a high confidence on -2 Standard dev trough Monday 
across western Great Lakes...however gefs tries to flatten out trough 
into a weak zonal flow. T850 indicate weak thermal ridge in wake of 
Hanna Mon/Tue. Most members forecast a sharp -2 Standard dev cold front 
across western Great Lakes SW into Central Plains Tuesday. Gefs forecasts 
arrival of front late Tuesday early Wednesday. It appears boundary tries to 
layout west-east orientation...as t850 fall off to single digits above 
zero Wed/thur. It appears thermal troughing will quickly depart and 
transition into some minimal ridging. 


Sun night through Monday afternoon appear to remain dry...then as frontal boundary 
arrives moisture pools eastward along and ahead of front and expect 
prcip to arrive late Monday/early Tuesday. Frontal passage may slow Tuesday so 
will advertise minimal chance for precipitation through afternoon hours. Next chance for 
precipitation at this time should arrive late week into the weekend...with yet 
another frontal boundary prognosticated to arrive Fri/Sat. 


&& 


Aviation /19z Saturday through Thursday/... 
IFR to MVFR ceilings and visibility expected through early this evening across 
the eastern third of the County Warning Area before ceilings and visibilities slowly lift to 
mainly VFR later tonight through Sunday. 


Northerly winds increasing to 15 to 25 kts with g35 kts will pose 
more of a mechanical turbulence issue rather than tru low level 
wind shear at our southeast taf sites (kmdt/kthv and klns). 


Residual ll moisture ascending the alleghenies could result in 
areas of IFR/MVFR ceilings at bfd and jst tonight. Otherwise...VFR 
conditions expected tonight through Monday as a ridge of high 
pressure builds in. A cold front will likely pass through the area 
Monday night or Tuesday...bringing with it scattered showers and 
thunderstorms. Hi pressure is expected to build in for 
for Wednesday through Friday...accompanied by good flying conds. 


&& 


Hydrology... 
heaviest rainfall of around 3 inches thus far has been focused 
across York County and points just to the north...while rains of 1 
to 2 inches has occurred elsewhere across the lower susq valley 
and surrounding counties. 


Another 1 to 2 inches expected from the lower susq main Stem to the 
ecent mountains this could bring some minor flooding problems to the 
smaller streams and creeks...but it appears that the larger 
streams will handle this distribution of rainfall and runoff with 
just 3/4 bankfull rises. 


&& 


Ctp watches/warnings/advisories... 
Flood Watch through Sunday afternoon for paz057>059-064>066. 
Wind Advisory until midnight EDT tonight for paz057>059- 
064>066. 


&& 


$$ 
Synopsis...Lambert 
near term...Lambert 
short term...Lambert 
long term...beachler 
aviation...Lambert 
hydrology...Lambert