000 FXUS61 KBOX 161750 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 150 PM EDT Tue Jul 16 2019 .SYNOPSIS... High pressure gives us another fair day as it moves off to the east. But heat and humidity will start to build. The remnants of Barry will pass just south of southern New England Thursday, but will bring showers and scattered thunderstorms, some with local downpours. High pressure builds for Friday through Monday bringing hot and humid weather. A couple of cold fronts will bring scattered showers and thunderstorms Sunday and Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 150 pm update... Partly sunny skies were resulting in a very warm afternoon but with rather comfortable humidity levels for mid July standards. Most locations were a few degrees from their expected high temperatures, which will generally range from the upper 80s to near 90, but a few locales in the lower CT River Valley may hit the lower 90s. It will be several degrees cooler across the high terrain and the immediate south coast, Cape/Islands with a southerly flow off the ocean. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Tonight... The warm front pushes across the region tonight, though it will be mainly dry. May see a few showers or even a rumble of thunder across the E slopes of the Berkshires this evening. Will continue to see deep layer moisture work across the region as H85 temps rise to +17C to +18C during the night. A weak short wave also moves along in the SW flow, so may see scattered showers and a few thunderstorms develop mainly around or after midnight across N central and western areas. Noting increasing instability as well, as K indices increase to the lower 30s and SLIs around -1. It will be sultry night with temps remaining mainly in the upper 60s to mid 70s, though a smidge cooler across the E slopes of the Berkshires. Wednesday... As a cold front slowly pushes S out of Quebec, it will push the remnants of Barry eastward. The front will tend to stall with the nearly zonal mid level steering flow in place. Instability continues to increase as CAPEs rise to 700 to 1100 J/kg (highest across NE CT/RI/interior SE Mass Wed afternoon), TQ values in the upper teens and K indices in the mid 30s. So, will see increasing chances for showers and thunderstorms across the region. Also noting PW values up to 2 to 2.5 inches, so should see some heavy downpours with some convection. Another warm, sultry day with dewpoints up to the lower 70s. Will see temps top off in the 80s once again across the majority of the region, though it will be a bit cooler across outer Cape Cod and the islands. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Big Picture... Zonal flow across the northern half of the nation while subtropical high pressure controls the southern half. Remnants of Barry lifting north will merge into the zonal flow between the Great Lakes and Ohio Valley, then move east with the zonal flow and crossing Southern New England Thursday. After it moves through, the subtropical high builds north over Southern New England for the weekend. Upper low pressure over the Gulf of Alaska dips south into the Pacific Northwest and then east with the zonal flow, approaching the Northeast USA early next week. Normal 500-mb heights for mid July are 580 to 582 Dm. Forecast heights are 585 to 588 Dm during late week, then build to 591 Dm over the weekend. Falling heights Monday. Expect warmer than normal temperatures through at least the weekend. General agreement among the model mass and thermal fields through Friday and possibly Saturday. The Sunday and Monday fields show small differences but generally favor continued hot temperatures. Forecast confidence is moderate-high. Concerns... Wednesday night to Thursday night... Northern stream shortwave moves through the zonal flow. This drives a cold front southeast through Southern New England Wednesday night. Remnants of Barry merge with the front over the Midwest. Model consensus shows the front moving through our area early Thursday morning, then stalling south of New England. The remnants of Barry then move along the front and pass just south of the region. Light flow Wednesday night becomes east-northeast Thursday as the low center passes to our south. This may try to stabilize the surface layer while convection moves over the top. Instability is marginal, shear is weak. Precipitable water values will be 2 to 2.5 inches Wednesday night and much of Thursday...this is above 2 std deviations above normal. Values may diminish north of the Mass Pike but even there expect values over 1.5 inches. The deep tropical environment suggests showers and scattered thunderstorms. Moisture values are high, and the moisture extends deep through the atmosphere. Lift is forecast about 30 mb/hr. This suggests potential for downpours and potential for street and poor- drainage flooding. Heaviest rainfall looks to be across parts of CT, RI and Southeast Mass during the day Thursday. The last of the remnants moves east of our area Thursday night, and drier air moves in above 700 mb. This should wind down the showers. However, a lingering surface flow out of the east may hold low clouds and widely scattered showers into Friday morning, especially across Eastern Mass. Friday through Monday... Note that the ECMWF and GGEM hold onto showers Friday morning in Eastern Mass before ending precipitation. Could be widely scattered showers lingering into the start of Friday. All models play with showers to our west and east Friday, but little or nothing over us. They also show a weak surface trough moving through. At the same time, we see the upper ridge building over the Northeast USA Friday and lingering over us Saturday. Temps at 700 mb are expected to reach above 10C Friday afternoon, peak around 13C Saturday, and linger above 10C until late on Sunday. Tend to favor a rain- free forecast for Friday and Saturday. Cold front then works through on Sunday and may support a few showers/tstms, mainly in Western MA. Mixing reaches to 850 mb each day. Temps at that level are at least 18-20C, and data for Saturday suggests 20-22C. So sfc max temps will be in the 90s each day, and could approach 100F on Saturday. Dew points will be 70 to 75 in this period, leading to heat index values of 95 to 103F Friday and Sunday...and 100 to 105F on Saturday. Heat Advisory headlines may be needed Friday to Sunday. A second cold front approaches on Monday with another round of shower/tstms especially in the west. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday night/... Tonight...High confidence. Mainly VFR conditions although can not rule out the low risk for some low clouds and fog patches near the south coast, Cape, and Islands toward daybreak. Wednesday...Moderate to high confidence. VFR conditions dominate. However, scattered showers and thunderstorms will develop during the afternoon. A few of the thunderstorms may contain locally strong wind gusts and torrential rainfall resulting in brief IFR-LIFR conditions. Wednesday night...Moderate confidence. The threat for showers and isolated thunderstorms will continue Wed night. The main concern will be for locally heavy rainfall focused near and south of the MA turnpike. Conditions will gradually deteriorate to MVFR-IFR thresholds as the threat for low clouds and fog patches increase. Lower conditions will also occur in the heavier showers. KBOS Terminal...High confidence in the TAF through Wednesday morning followed by moderate confidence Wednesday afternoon and night. The main concern will be for a few thunderstorms in the vicinity of the terminal from mid afternoon Wed into Wed evening. KBDL Terminal...High confidence in the TAF through Wednesday morning followed by moderate confidence Wednesday afternoon and night. The main concern will be for a few thunderstorms in the vicinity of the terminal from mid afternoon Wed into Wed evening. Outlook /Thursday through Saturday/...High confidence. Thursday through Thursday Night: MVFR in clouds and fog. Chance SHRA, slight chance TSRA. Friday: VFR. Slight chance SHRA, isolated TSRA. Friday Night and Saturday: VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. Today...S-SW winds around 10 kt with gusts 15-20 kt. Seas 3 feet or less. Good visibility. Tonight and Wednesday...SW wind 10 to 15 kt. Gusts up to 20 kt on the southern outer waters. Seas 4 ft or less. Visibility lowering to 3-5 NM in areas of showers Wednesday afternoon, with a chance for thunderstorms. Outlook /Wednesday Night through Saturday/...High confidence. Wednesday Night: Winds less than 25 kt. Rain showers likely, chance of thunderstorms. Thursday through Thursday Night: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms. Friday: Winds less than 25 kt. Slight chance of rain showers. Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers, isolated thunderstorms. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. && .CLIMATE... Record highs for Wednesday July 17 are as follows: BOS: 98F in 1977 & 1999 BDL: 97F in 1999 PVD: 97F in 1977 & 1999 ORH: 93F in 1900 Record highs for Saturday July 20: BOS: 99 in 1991 BDL: 100 in 1991 PVD: 101 in 1991 ORH: 92 in 1901 Record highest min temps for Saturday July 20: BOS: 75 in 2016 BDL: 73 in 1975 PVD: 77 in 1983 ORH: 72 in 2013 Record highest min temps for Sunday July 21: BOS: 81 in 1991 BDL: 74 in 1977 PVD: 77 in 1980 ORH: 73 in 1991 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/EVT NEAR TERM...Frank SHORT TERM...EVT LONG TERM...WTB AVIATION...Frank/WTB MARINE...WTB/EVT CLIMATE...