Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 270618 AFDCTP Area Forecast Discussion National Weather Service State College PA 218 AM EDT Sat May 27 2017 .SYNOPSIS...
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A trough of low pressure is expected to move across southern PA this morning and keep a warm front just to the south of the state. A cold front will approach the region Sunday, and pass through Sunday night and early Monday. Low pressure will stall over northern Ontario mid-week and create a slightly cooler than normal and unsettled stretch of weather.
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&& .NEAR TERM /THROUGH TODAY/...
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sky clear over much of the area but the north is still stuck in the low stratus. The clouds are retreating to the north a bit, but there is a big mass of cirrus and lowering cloud cover as two clusters of convection move in from OH. These areas of storms continue to weaken - with little to no lightning left in them. The residual showers/anvil rain will pass through the SW portion of the CWA this morning. Dewpoints overhead and over MD/WV are only in the 50s, and stability argues against mentioning the T word at this point. Some rain may arrive in the Laurels before 09Z, but the more-likely time for rain to begin in the west is after sunrise (10Z). The rain should slink to the SE and be out to the east of the area just after noon. Places N of FIG-UNV-SEG will likely stay dry, and POPs will be held below 50pct there. But, we will still mention some as the flow could still make some sprinkles up that-a-way. The afternoon looks nice with increasing sunshine from the west to the east. The proximity of the warm front just south of the state will mean some cloudiness is expected to linger across the S. Will keep just a 20 POP S of the Turnpike for the aftn. The chc for thunder does exist along the MD border, so we will just mention it only there for now, as SPC does just nick us with MRGL risk mention for any aftn convection. Maxes will be within a deg or two of 70F. So, take a break from heating/cooling the house today. Get out and enjoy an afternoon picnic.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM SUNDAY/...
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Clearing across the north this afternoon and evening will last into or even through the entire night. However, the low level flow will turn to the SE here in PA (north of the warm front). This could allow crud (aka low stratus clouds) to creep in from the south/east. The more-likely places to see the low clouds will be right along the MD border and up into the Laurels where upglide due to the elevation change will help aid in cooling and condensation. Mins will be Will start to mention a little DZ possible there, but keep POPs almost nil tonight and Sun AM. As the flow becomes more southerly in advance of the storm approaching from the west, the chance for storms increases on Sunday afternoon. The destabilization will be easiest in the east where less low clouds are expected, but the deeper moisture is off to the west and the dynamics are even farther to the west. Will ramp POPs up in the west through the aftn, leaving the east in chc or less POPs.
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&& .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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A quick transition to increasing deep layer moisture and higher PWAT air of 1-1.25 inches will occur late Sunday. A large-scale trough and increasing upper level divergence (associated with a lead upper shortwave in the west/SW flow) will lead to a fairly large area of moderately strong uvvel and a widespread moderate rainfall along and ahead of a cold front. GEFS Probs for GE 0.50 inch of rain/24 hours ranges from 50-80 percent across the wrn mtns of PA...to generally less than 50 percent across the eastern half of the state. This translates into very high POPs for measurable rain (90 percent or more) across the western half of the CWA, to between 70 and 90 percent across the south-central mtns and Susq Valley. 12Z EC and 12z GEFS are in very good agreement on the timing/location of the north/south sfc cold front during the afternoon hours Monday across the eastern half of the state with weak deep- layer ridging and drying for Monday afternoon and night. Dry conditions expected Tuesday morning before significant cooling aloft accompanies a pair of short waves late Tuesday and later Wednesday. POPs during this midweek period will be painted as chc - translating to scattered showers with preference for the majority of the QPF (albeit quite light at that)to be across the typical west-nwrly flow upslope prone areas of the Laurel highlands and NW mtns. The chance for any thunder will be very minimal Tuesday through Thursday. Generally dry NW flow occurs late in the week into next weekend as a 1020 sfc high over the upper midwest Friday evening builds SE twd the region. Pops Thur night through Fri night will be 30 percent or less. After our bout of coolish weather with temps several Deg F below normal Sunday and Monday, GEFS mean temps rebound back to near or slightly above normal (even under slightly cooling 850 mb temps) for Tuesday through at least Thursday. ECENS mean temps are several deg warmer than the GEFS and Nat`l Blend of Models temps. leaned closer to the cooler solutions based on the few-svrl deg C of cooling aloft with near to slightly below 850 mb temps.
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&& .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... Pool of cold air aloft and associated low level instability is resulting in persistent MVFR stratocu across the northwest mountains late this evening. Bigger concern will come late tonight, as skies clear and wind becomes calm, likely resulting in areas of fog. Latest dewpoint depressions, as well as model guidance, target BFD for the best chance of significant vis reductions. However, can`t rule out some fog toward dawn at UNV or IPT. Increasing mid level cloudiness should limit the fog potential over the southern airfields. Probability of at least tempo IFR visibility at BFD is about 70 pct late tonight. Remnant meso/convectively enhanced wave tracking east across the Ohio Valley should thicken clouds back up by Saturday morning. As this feature moves through, expect a period of rain to affect primarily central/southern Pa between 12Z-18Z, probably not falling heavy enough to significantly reduce visibilities. Latest SREF prob charts and model soundings indicate MVFR cig reductions are likely at JST and possible, but not likely, elsewhere. .OUTLOOK... Sun...AM fog possible. Evening showers/reduced cigs possible west. Mon...AM showers/low cigs possible. Tue...No sig wx expected. Wed...Slight chance of showers/reduced cigs. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Dangelo/Gartner LONG TERM...Lambert AVIATION...Fitzgerald

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