Area Forecast Discussion
Issued by NWS Binghamton, NY

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173 FXUS61 KBGM 221956 AFDBGM Area Forecast Discussion National Weather Service Binghamton NY 356 PM EDT Sun Jul 22 2018 .SYNOPSIS... A warm and muggy night is expected across the region with scattered showers and thunderstorms especially over northeast Pennsylvania, the southern tier and southern Catskills. A deep southerly flow of very moist air will reside over the region through Thursday. Showers and thunderstorms are expected through the period with the activity most widespread during the daylight hours. The thunderstorms will produce heavy downpours. && .NEAR TERM /THROUGH MONDAY NIGHT/... At 330 PM...local radar indicated just isolated to scattered activity across northeast Pennsylvania and the southern Catskills. A mid level short wave lifting north from southeast Pennsylvania will increase the convective coverage in northeast Pennsylvania, the southern tier and western Catskills through the early evening hours. Any thunderstorms will be capable of heavy downpours which could lead to poor drainage and urban flooding. Late tonight there will be a lull in the activity before embedded mid level short waves in deep southerly flow toward daybreak bring more convective activity into northeast Pennsylvania. Overnight lows will range in the mid 60s to lower 70s. Monday through Monday night...A deep south/southeast flow of very moist air will continue over the region as an upper level low continues dropping south into the Tennessee Valley while an upper level ridge resides in the western Atlantic. A combination of embedded mid level short waves and diurnal instability will increase convective coverage by mid/late morning through the evening hours. Precipitable water values increase to around 2 inches by the afternoon and model soundings indicate tall/skinny CAPE along with warm cloud layer above 10k feet. This all indicates the potential for very heavy downpours with any thunderstorms and will include in the forecast from mid morning through the evening hours. No flood watches planned yet but if training convection occurs during the next several days a watch may be needed. Highs on Monday will range in the upper 70s to mid 80s and with dewpoints around 70 is will feel rather uncomfortable. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... 430 AM Update... The latest guidance continues to be in excellent agreement for the overall pattern in the short term period. An upper level low will remain nearly stationary over the Southeast US during this timeframe; at the same time a building upper level ridge will be centered off the New England Coast, out over the North- Atlantic. The circulation around these two features will pull deep, tropical moisture northward from the central Caribbean and Bahamas region. With these features remaining nearly stationary, a prolonged stretch of tropical moisture transport is progged to impact the area. As the upper ridge flexes westward a bit Monday night...this will place the best tropical moisture feed from eastern North Carolina, to Washington DC, up into Northeast PA and Central NY. In the heart of this enhanced moisture feed PWATs are now forecast to be between 2-2.25 inches, along with dew points around 70...a very humid air-mass. This conveyor belt of tropical moisture basically waffles back and forth across our CWA through the short term period, with little overall movement. The guidance is indicating that waves /disturbances will move from south to north embedded within this deep moisture feed...these waves will provide ample lift for periods of showers and thunderstorms to impact our area. With confidence growing, bumped PoPs up into the likely category Monday night through Tuesday night. Exact rainfall amounts are difficult to forecast this far out, but the potential is certainly there for showers/storms to produce heavy rain. 12 hour basin average QPF amounts are expected to range from 0.25-0.50" Monday night, 0.33-0.75" Tuesday (highest west) and 0.25-0.75" Tuesday night (highest west)...but there could certainly be much higher amounts locally. WPC has placed parts of our forecast area in a slight risk for excessive rainfall Monday night into Tuesday...indicating a 10-20 percent chance for rainfall amounts to exceed flash-flood guidance. The mid-level flow is well aligned from south to north across the region in the 850-500mb layer, with mean layer winds between 30-40 kts forecast...therefore showers and thunderstorms have the potential to train over the same areas. This period will need to be monitored closely for the heavy rain and flooding /flash-flooding potential. The pattern continues to look very similar to the end of June 2006...so the heavy rain potential is certainly there. Daytime instability parameters are expected to be around 500-1000 J/Kg of MLCAPE, with modest LIs around -4. Deep layer shear values are higher Monday evening, between 30-40 kts...so cannot rule out a few stronger storms. By Tuesday 0-6km shear decreases to between 20-30 kts....so it would seem there is a lower chance for well organized severe weather Tuesday. Outside of the showers and thunderstorms expect mostly cloudy skies, warm and humid conditions through the period. Overnight lows will be in the mid-60s to lower 70s both nights...with daytime highs in the upper 70s to lower 80s Tuesday afternoon. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... 430 AM Update... By Wednesday, the latest guidance shows heights falling as an upper level trough slowly approaches from the Great Lakes. This will only act to further enhance the sub-tropical moisture feed, increasing lift and instability across our area. PWATs remain at or above 2" through the day. Therefore, Wednesday looks to feature widespread showers and thunderstorms, with heavy rainfall being the main concern once again. With excellent model agreement, went ahead and bumped PoPs up into the categorical range Wednesday into Wednesday night, as the front very slowly pushed east. It is now looking like Wednesday into Wednesday night could feature the heaviest rain and greatest potential to see flooding and/or flash-flooding. Exact details of where the heaviest rain sets up, and exactly how much rain will fall remain uncertain...but the pattern is favorable for torrential downpours. By Thursday morning, the initial front will be over the far eastern portion of our forecast area, with showers and thunderstorms lingering here. PWATs should begin to come down behind this boundary, as the tropical air-mass shifts east...but showers and t`storms will still remain likely areawide as instability increased under the influence of the slow moving upper level trough. Thursday is looking a bit warmer, as the area perhaps sees occasional breaks of sunshine. Highs are now forecast to reach 80-85 in most locations, dewpoints hold in the mid to upper 60s.Thursday night features just a chance for a shower or thunderstorm under partly cloudy skies. Lows hold in the 60s. On Friday, a secondary frontal boundary will work through the area from west to east during the day. Instability will remain sufficient out ahead of this front for scattered thunderstorm development. The amount of convection the area sees on Friday will be highly dependent on the timing of this front...if it moves through during the morning there may not be enough time for much t`storm development...as opposed to if if moves through during the afternoon or evening. The timing remains uncertain at this point. PWATs and dew points continue to lower as the humid air mass moves east. By Friday afternoon look for dew points in the lower to mid-60s with temperatures reaching the upper 70s to lower 80s again. There remains a lot of uncertainty for Saturday and Saturday night, as the latest GFS stalls the frontal boundary across northern PA, bringing additional periods of showers and t`storms to our area. Meanwhile, the 00z ECMWF push the front further south/east...allowing for drier weather. With the lower confidence decided to take a blend of the latest guidance for now, until models can converge on a common solution. Temperatures look to be very close to the seasonal average, with lows in the lower to mid-60s Friday night and highs 75-82 Saturday. && .AVIATION /20Z SUNDAY THROUGH FRIDAY/... A very moist airmass will reside over the region through this TAF period. Through early evening MVFR/low VFR ceilings will continue with a chance for MVFR showers at KAVP/KELM through early evening. Overnight, ceilings will lower into the MVFR/Alternate Required category. Monday morning slow improvement to MVFR/low VFR will occur during the mid/late morning. Scattered showers and thunderstorms will occur overnight and into Monday morning but coverage not widespread enough to include in TAF. By Monday afternoon MVFR/Alternate Required showers and thunderstorms are likely at all terminals. East to southeast winds at 10-15 knots with gusts around 25 knots decreasing this evening to 5-10 knots. East/southeast winds again Monday increasing to 10-12 knots with gusts around 20 knots. Outlook... Monday night through Thursday...Occasional restrictions likely, with periods of showers and thunderstorms. Thursday night/Friday...Brief restrictions possible in scattered showers and thunderstorms. && .BGM WATCHES/WARNINGS/ADVISORIES... PA...None. NY...None. && $$ SYNOPSIS...RRM NEAR TERM...RRM SHORT TERM...MJM LONG TERM...MJM AVIATION...RRM

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