Area forecast discussion National Weather Service Taunton Massachusetts 720 PM EDT Sat may 18 2013 Synopsis... high pressure across northern New England will move off the coast Sunday. A warm front will move through the region Sun night...probably bringing a few showers. The front will lift north of the region early next week and then stall over New York and central New England. Weak waves of low pressure will move along the front middle of next week bringing warmer...more humid conditions along with scattered showers as well as possible thunderstorms...most likely during the afternoon and evening hours. && Near term /until 6 am Sunday morning/... 7 PM update... Inverted high pressure ridge nosing into the box County Warning Area this evening...which has allowed middle and high level clouds to sink closer to the S coast of RI/CT. Therefore...with loss of diurnal heating expect a bit of breaks in the clouds tonight until a shortwave allows for increasing cloudiness from the SW during the morning hours. Min temperatures a bit warmer tonight given the warmer start...increasing middle level temperatures under warm advection and increasing moisture in the column during the overnight hours. Continued with previous forecaster/S thinking and held off the -shra activity until well after daybreak...slower than guidance currently suggests. && Short term /6 am Sunday morning through Sunday night/... Sunday... high pressure moves off the New England coast as a warm front slowly approaches from the south. This will result in middle level warm advection and an increase in cloud cover. There still will probably be a few peeks of sun at least in the morning...but the overall trend will be for mostly cloudy skies. High temperatures are tricky and will depend upon just how quickly skies become mostly cloudy. We blended the cooler gfsmos guidance with the much milder metmos. Best chance of the mildest readings will be across the Merrimack valley...away from the coast and where skies will be slower to become mostly cloudy. Will range highs from the middle 60s to around 70...but later shifts may have to make tweaks overnight. As for precipitation chances...better focus/forcing/moisture will remain to our south and west. Therefore...expect most of the day will feature dry weather. Warm advection may still result in a few spot showers at times...with the best chance in our southwest zones. Therefore...will include some low probability of precipitation to cover this potential across most areas. Sunday night... the warm front gradually lifts north across southern New England. Middle level forcing/dynamics are not that impressive...so not expecting a lot of rainfall. However...still expect some scattered showers in the warm air advection pattern. Can/T rule out some isolated thunder south of the Massachusetts Turnpike...but indices were too marginal to insert at this Point. May also see some patchy fog develop as higher dewpoint air overspread the region. Low temperatures should only fall into the lower to middle 50s given increasing low level moisture and cloud cover. && Long term /Monday through Saturday/... highlights... * warm and humid with scattered showers through at least Thursday Overview and model preferences... 18/12z long range guidance suite is in fair agreement through the middle term period...but then struggles with the merging /or non- merging/ of a split flow regime toward the end of the period. Given the agreement that the convergent region of these two streams will dominate through the middle term...will use a GFS/European model (ecmwf) blend to baseline forecast. For the tail end of the long term...will likely lean away from the European model (ecmwf) deterministic run...as it generates a very deep meandering cutoff in northern New England which would suggest that unsettled conditions continue well into /and possibly beyond/ the weekend. In any case...with convergent streams aloft through the middle term...unsettled conditions are likely...but as was noted...it should not be a washout. Details... Monday into Monday night... surface warm front shifts into northern New England with time...allowing much of southern New England to break into the warm sector through the period. Looks like a fair amount of moisture will combine with diurnal heating to yield some daytime -shra...particularly over southern New Hampshire an northern Massachusetts. Soundings look to remain fairly stable during the day...so will keep thunder out of the forecast for now. With high temperatures in the upper 60s to near 70 and dewpoints in the upper 50s...conditions are likely to feel muggy. Tuesday into Wednesday... the warm front in northern and central New England is expected to gradually sink S of the region through the period. On Tuesday...this frontal passage /particularly during the afternoon heat/ expect some destabilization...especially if there are some early day cloud breaks as some of the guidance suggests. Cooling upper levels as high pressure noses in from the north suggest a rise in k/tt and Li/S dipping to 0 to negative values. Shear is not great...particularly through 850 mb...but there is enough support for updrafts...so will continue to suggest thunder for Tuesday. On Wednesday...weak early day ridging will likely yield a partly cloudy start to the day until return flow develops as high pressure slides to the NE. Given the approaching shortwave...early clearing and increasing moisture...may see another day with the threat for thunderstorms...especially in the west as a secondary warm front moves through the area. A little better shear on Wednesday too possibly...so will continue with a thunder threat on Wednesday as well. Thursday and Friday... tricky forecast here as it will be dependent on how quickly northern stream jet energy sinks S from Quebec and Ontario. This will dictate how quickly a series of shortwaves and their surface low pressure waves will affect the region. In any case...the wet weather continues although a bit more stable than Tuesday and Wednesday. Given the differences between models in how the northern stream works out...exact timing for any of these waves remains a bit of a question mark. Once again...it will likely not rain everyday...but there is the threat for at least -shra through the period. The weekend... the southern stream ridge begins to move the northern stream longwave trough offshore through the period...so looks like a transition to more dry weather will be likely sometime during the weekend. && Aviation /00z Sunday through Thursday/... forecaster confidence levels... Low...less than 30 percent. Moderate...30 to 60 percent. High...greater than 60 percent. Overview...high confidence continues tonight. Moderate confidence Sunday and Sunday night. Overnight... expecting mostly VFR conditions during the overnight hours. Low confidence in some MVFR ceilings arriving in the CT valley toward daybreak. Sun... continued with optimistic forecasting suggesting the MVFR ceilings take until middle morning to early afternoon to arrive in the interior...holding off until evening for eastern terminals. Therefore...mostly VFR to start...with a gradual downward trend through the day. Sun night... mainly MVFR/IFR in a mix of fog and showers during the overnight hours Kbos terminal...high confidence in taf overnight and early in the day tomorrow. Lower confidence in timing of MVFR by sun evening...then IFR by overnight in fog/showers. Kbdl terminal...moderate confidence in taf overnight...mainly in potential for MVFR ceilings to arrive at terminal by Sun morning. It appears best chance will be middle day Onward sun. Therefore...VFR expected to dominate into the morning. Outlook...Monday through Thursday... Moderate confidence through the period. Mainly VFR/MVFR during the days...with the best chance for MVFR in any daytime showers or occasional thunderstorms. Expect mainly MVFR/IFR during the overnight hours in a mix of fog and low stratus...especially closer to the South Coast. In sum...a period of unsetteled weather is expected through the period. && Marine... forecaster confidence levels... Low...less than 30 percent. Moderate...30 to 60 percent. High...greater than 60 percent. Moderate to high confidence through Sunday night. Relatively weak pressure gradient should keep winds/seas below Small Craft Advisory thresholds tonight and Sunday. However...high pressure moving off the coast on Sunday will begin to generate long southwest fetch into the southern waters. This should allow seas to build to Small Craft Advisory thresholds across our southern outer-waters Sunday night. Have hoisted Small Craft Advisory headlines for hazardous seas in this region. Small Craft Advisory headlines may have to be expanded into some of the southern sounds...but since its a 3rd period event confidence was not high enough to do at this point. Outlook...Monday through Thursday... Moderate confidence through the period. Winds should remain below Small Craft Advisory thresholds through the period. Also...a combination of showers and fog will likely lead to reductions in visibilities through the period. Monday into Tuesday...lingering swell along the southern waters and eastern outer waters gradually subsides through Tuesday. Will likely need Small Craft Advisory for seas into the day Tuesday. Wednesday and Wednesday night...seas remain below small craft thresholds. Thursday...as low pressure approaches from the west. Expect gradually building seas...which may reach 5-7 feet during the day Thursday. Small craft advisories may be needed again. && Box watches/warnings/advisories... CT...none. Massachusetts...none. New Hampshire...none. Rhode Island...none. Marine...Small Craft Advisory for hazardous seas from 11 PM Sunday to 8 am EDT Monday for anz254-255. Small Craft Advisory for hazardous seas from 5 PM Sunday to 8 am EDT Monday for anz256. && $$ Synopsis...Frank/doody near term...doody short term...Frank long term...doody aviation...Frank/doody marine...Frank/doody/Thompson