textproduct: Caribou

WHAT HAS CHANGED

Updated aviation section for 12z TAF issuance

The Storm Prediction Center has added a low chance for an isolated tornado to northwestern Maine but maintains the marginal risk.

Issued SCA for the intra-coastal waters from this afternoon through Wednesday afternoon. Extended the SCA on the coastal ocean waters through Wednesday night.

KEY MESSAGES

1) Isolated to scattered thunderstorms this afternoon, mainly across northern areas, could be accompanied by isolated stronger wind gusts.

2) A widespread rainfall is expected late Tuesday night into Thursday morning, which will continue to improve the long term drought. The ponding of water in known poor drainage areas is possible.

3) There is a slight chance for strong thunderstorms across the North Friday afternoon.

4) There is the potential for another widespread soaking rain from late Sunday into Monday. This should continue improvement in the drought.

DISCUSSION

KEY MESSAGE 1... Isolated to scattered thunderstorms this afternoon, mainly across northern areas, could be accompanied by isolated stronger wind gusts.

KEY MESSAGE 1 DESCRIPTION... The Storm Prediction Center has placed northern and central Maine in a marginal risk for severe thunderstorms today. Ahead of an approaching cold front, thunderstorm are expected to develop over eastern Quebec province and move eastward into northern and central Maine. Daytime heating should contribute to steep low-level lapse rates which in combination with sufficient low-level moisture advection should favor some weak surface based instability of around 500 J/kg. The main concern from these storms is gusty winds as a result of several factors including dry low-levels as represented by an inverted v sounding and relatively strong winds at the top of the boundary layer that could easily be mixed down to the surface.

Models are currently showing fast moving bowing structures this afternoon which is reasonable given the strong, deep-layer wind field. Such a convective complex is quite favorable for strong winds. A few models show some transient supercell structures and helicity tracks as a result of the strong low-level shear profile. The Storm Prediction Center highlights a low risk of a tornado which cannot be ruled out given the kinematic environment but thinking this is a relatively low chance given the relatively high LCLs and very limited instability.

KEY MESSAGE 2... A widespread rainfall is expected late Tuesday night into Thursday morning, which will continue to improve the long term drought. The ponding of water in known poor drainage areas is possible.

KEY MESSAGE 2 DESCRIPTION...

A cold front will pass through the state Tuesday night before stalling over the area Wednesday. A steady, soaking rain will develop over the area Tuesday night and intensify Wednesday as a wave of low pressure develops along the boundary.

A mean northern stream trough continues to build into the northeastern U.S. Wednesday night and Thursday. A strong shortwave embedded in the flow is expected to move into the area Wednesday night, then exit into the southern Maritimes Thursday. At the surface, a broad area of low pressure crosses southern Maine Wednesday night, then exits into the eastern Maritimes on Thursday allowing a frontal boundary to finally push offshore.

With the region still under a coupled jet structure, being in the right rear quadrant of a 120+ kt upper jet to the north/northwest and the left front quadrant of a 140+ kt upper jet to the southwest, will see enhanced lift. This will be re- enforced by a secondary maxima in the low level jet passing just offshore Wednesday night. The combined forcing form the upper and low level jet will enable moderate to possibly locally heavy rainfall across the region Wednesday night. The rain should taper off from NW to SE from late Wednesday night through Thursday morning. In addition, with showalter indices across Downeast Maine of 2 to 4, have added in a slight chance of (elevated) thunder across Downeast Maine Wednesday evening.

At this time, expect 1 to 1.5" across most of North, except for 2/3 to 1" across far western portions, and 1.5 to around 2" of rain across elevations above 2000 ft in the Central Highlands. Across Downeast Maine 0.5 to 1" of rain is forecast. Locally higher amounts are possible, especially in those areas experiencing embedded convection. Especially across the North and in those areas experiencing locally heavy rainfall, the ponding of water in known poor drainage areas is possible.

Even with a 60-65kt low level jet passing just offshore Addends night, there should be a sufficient low level inversion to allow for any significant wind gusts outside of any isolated stronger convection. As a result, no wind headlines are needed with this system.

KEY MESSAGE 3... There is a slight chance for strong thunderstorms across the North Friday afternoon.

KEY MESSAGE 3 DESCRIPTION... Steep low level lapse rates across the region due to a passing low-mid level cold pool should produce sufficient instability to cause isolated to scattered showers with possibly a rumble or two or thunder. The best chance for any thunderstorms is across the North, where the coldest air in the low levels will be. At this time, do not expect any storms to be severe, however some could be strong, with small hail and gusty winds.

KEY MESSAGE 4... There is the potential for another widespread soaking rain from late Sunday into Monday. This should continue improvement in the drought.

KEY MESSAGE 4 DESCRIPTION... Shortwaves embedded in the mean northern stream trough over the eastern U.S. Sunday and Monday could result in another area of low pressure crossing the region, moving along a slow moving frontal boundary. While the models differ on the timing of this, there is general agreement on the occurrence of this. Therefore, there is the potential for another widespread soaking rainfall from late Sunday into Monday. At this time, it is a little to early to specify any amounts, but it looks like there is a decent chance that this should result in continued improvement to drought conditions across the region.

AVIATION /10Z TUESDAY THROUGH SATURDAY/

Tuesday...VFR, except MVFR possible in afternoon showers and isolated/scattered thunderstorms at the Aroostook terminals. Added PROB30 for the northern terms for the -TSRA potential. S to SW wind 10 to 20 kt with gusts 30 kt. Low level wind shear expected at BHB and possible at all other terminals but confidence too low to include in TAF.

Tuesday night...MVFR with IFR possible KBGR/KBHB. S to SW wind 10 to 15 kt. LLWS expected all terminals early.

Wednesday...Predominantly MVFR with periods of IFR. Greatest chance for IFR at southern terminals. -RA. S winds 5 to 15 kts, strongest south where gusts up to 25 kts are possible. LLWS possible, mainly southern terminals.

Wednesday night-Thursday: IFR or lower likely, improving to VFR from NW to SE from late Wednesday night through Thursday morning. NW winds G15KT possible at northern terminals late Wednesday night. LLWS likely at southern terminals Wednesday night.

Thursday night: VFR. NW winds G15KT possible Thursday evening.

Friday-Friday night: VFR, with a low chance of MVFR at northern terminals in any stronger convection/thunderstorms. Stronger convection/thunderstorms could result in small hail and gusty winds. WNW winds G15KT possible Friday afternoon.

Saturday: VFR, with a very low chance of MVFR in any showers. SE-S winds G15-20KT possible. Saturday afternoon.

MARINE

Low end gale conditions expected on the outer waters this evening through late tonight with seas peaking at 9 to 12 ft. Waves decrease Wednesday. SCA conditions expected through Wednesday on the coastal and intracoastal waters. Seas peak at 8 to 10ft on the coastal waters and 6 to 8 ft on the intracoastal waters tonight.

SCA conditions expected to continue on the coastal ocean waters Wednesday night, so have extended the SCA through 10z Thursday. SCA conditions are also likely on the intra-coastal waters, but confidence in this is not quite high enough to have an SCA there at this time. Gusts should be just below gales on the outer waters Wednesday night. SCA conditions could linger into Thursday on the coastal ocean waters Thursday, with sub-SCA conditions on the intra-coastal waters. The outer waters should continue to see gusts below gale force on Thursday. All waters should see sub-SCA level winds and seas Thursday night-Friday. SCA level seas could return to the coastal ocean waters Friday night and Saturday, with no headlines forecast for the intra- coastal waters and outer waters Friday night-Saturday.

CAR WATCHES/WARNINGS/ADVISORIES

ME...None. MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ050-051. Small Craft Advisory from 2 PM this afternoon to 6 PM EDT Wednesday for ANZ052. Gale Warning from 4 PM this afternoon to 3 AM EDT Wednesday for ANZ080-081.