textproduct: Gray - Portland

WHAT HAS CHANGED

No significant changes with this forecast.

KEY MESSAGES

1. Cool weather will continue through Thursday night. Can't rule out some snowflakes overnight with a return to dry weather Thursday.

2. A moderating temperature trend continues with mainly dry conditions from late week into the weekend. These drier conditions may allow for increasing fire weather concerns this weekend.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION...

The cool pattern continues overall. Model guidance is pretty insistent that warm advection over the top of the low level cold will result in shower activity this evening and overnight. It also forecast that for much of today and that has not panned out. So I knocked PoP down to high chance overnight to mention scattered showers. Showers look a little more likely along the front as it sweeps out to sea early Thu morning. So I left PoP alone there. Overall it will be a light precip event, unlikely to lead to a wetting rain, but I would not be surprised to see some flakes mixing in at times and maybe even all snow in the higher terrain over western Maine.

Thu afternoon will be a little bit warmer, closer to normal for this time of year. It will also return us to dry weather. I did mix in some lower dewpoints as is the norm for the spring pre-green up. Given the clouds over eastern zones and cooler temps, the only locations dropping below 30 percent RH are across the southern half of NH. Winds will also be breezier, with northwest gusts of 25 to 30 mph possible. So elevated fire weather conditions are possible.

KEY MESSAGE 2 DESCRIPTION...

A 500mb low will be centered just east of the region on Friday, and a shortwave stemming from this low will dive southward during the day. This should bring mostly just an increase in diurnal cloud cover as the atmosphere looks generally too dry to support precip, but there may still be enough moisture for isolated showers over parts of western Maine. Forecast soundings show steep low-lowel lapse rates, around 100 J/kg of MUCAPE and cold temperatures aloft, so can't rule out the possibility of small hail or graupel if any showers do form. Farther north in the western ME mountains, some of these may be mixed with snow. Otherwise, highs will be mostly in the 50s, except 40s across the north.

Ensembles then continue to favor a stretch of mostly dry weather over the weekend into early next week with temperatures fairly close normal for this time of year ranging from the mid 50s to lower 60s and lows in the 30s to lower 40s. One thing to watch for an area of low pressure on Sun-Mon that may bring a few showers with it, but most guidance is currently in favor of the low staying more to the south and west. This stretch of mostly dry weather could bring increasing fire weather concerns, but fortunately winds look generally light.

There is a better signal for more in the way of wet weather toward the middle of next week with upper ridging shifting off the east and more of a troughing pattern developing over the Northeastern CONUS. The GFS and ECMWF are in pretty good agreement with a cold front approaching and increasing shower chances in the later Tuesday into Wednesday timeframe.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Through 18Z Thursday...Difficult aviation forecast thru Thu. Widespread MVFR right now, but guidance is quite pessimistic overnight. There are two camps, MVFR and widespread IFR or lower. Right now guidance thinks it should be IFR, so I am leaning towards keeping most sites MVFR thru the night. The exception will be AUG/RKD where IFR CIGs will start to creep in after sunset. There will also be scattered showers this evening and overnight across western Maine. I think ultimately some lower VIS is fog is more likely than showers reducing VIS. Conditions will scatter out to VFR by Thu afternoon.

Outlook:

Thursday Night: VFR conditions expected.

Friday-Saturday: Mainly VFR. Isolated showers possible Friday afternoon in the vicinity of AUG and RKD.

Sunday-Monday: Low pressure may bring rain showers to the area Sunday and/or Monday. However, it currently looks like there is a better chance the low and showers stay south of the area, and conditions remain VFR.

MARINE

Some marginal SCA gusts are possible on the coastal waters this afternoon, but otherwise winds and seas are expected to remain below SCA thresholds into Fri. There will be warm advection and moisture pooling tonight as a weak system moves thru the area. Some indications that fog may try and form ahead of the cold front, and right now this would most likely affect the waters north of Port Clyde into Penobscot Bay if it occurs.

Friday-Wednesday...Conditions are expected to remain below SCA levels across the bays and coastal waters through this weekend and early next week. Low pressure may approach the region toward the middle of next week to bring some increase in winds and seas.

FIRE WEATHER

Scattered showers are expected thru tonight, but the chances of a widespread wetting rain event are low. As a result the return of dry weather and gusty winds Thu will lead to some areas of southern NH dropping below 30 percent minimum relative humidity with wind gusts of 25 to 30 mph. Winds diminish a little Fri but remain breezy with the area of sub-30 percent minimum relative humidity expanding northeastward into western Maine. Dry weather looks to continue thru the weekend.

GYX WATCHES/WARNINGS/ADVISORIES

ME...None. NH...None. MARINE...None.