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000 
FXUS61 KBOX 200830
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
430 AM EDT Thu Sep 20 2018

.SYNOPSIS...
High pressure builds into New England through tonight yielding 
dry cool weather. Warmer temperatures, gusty winds and more 
humid conditions expected Friday ahead of an approaching cold 
front. The front may bring a few showers and thunderstorms 
Friday night into early Saturday, then large high pressure will
bring dry but cool conditions through the weekend into early 
next week. Another warm front may approach late Tuesday into 
Wednesday with scattered showers and possibly a few 
thunderstorms.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
High pres builds south into New Eng as heights rise on northern
periphery of building east coast ridge. However, continued moist
NE flow will likely maintain cloud cover through the morning,
especially across eastern New Eng, and some drizzle or a brief 
shower is possible over Cape/Islands. Developing sunshine in the
west should overspread eastern New Eng this afternoon as low
level moisture decreases. 

Highs will be mostly in the mid/upper 60s, except lower 70s CT
valley where 925 mb temps are milder. NE winds will diminish
over Cape/Islands.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Tonight...

High pres remains in control as it shifts east of New Eng 
overnight. NAM/GFS indicate increasing low level moisture 
returning which will likely lead to stratus and patchy fog 
developing. HREF shows highest probs of stratus and fog in the 
interior and can't rule out some patchy drizzle. Otherwise, dry
weather with lows in the 50s. 

Friday...

Increasing S/SW flow develops ahead of approaching cold front
which moves into the eastern Lakes toward evening. Expect a mix
of sun and clouds and becoming breezy in the afternoon. 
Instability is nil on Fri. Axis of instability and forcing 
remain well to the west so a dry day is anticipated. A line of 
convection may be moving into western NY toward evening.
Southerly flow and shallow mixing depth will limit heating with
highs mainly in the lower 70s coastal plain and interior 
valleys, but humidity will be increasing as dewpoints climb 
into the 60s in the afternoon.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...

Highlights...

* A cold front will bring scattered showers and a few 
  thunderstorms especially across the interior Friday night
* A large high builds across from central Canada Saturday 
  afternoon into Monday with cool but dry conditions
* Another frontal system may approach late Monday night or 
  Tuesday with showers and a few thunderstorms, which may linger
  into mid week
  
Overview...

00Z model guidance continues to signal a changeable weather 
pattern across the northeast U.S. for most if not the entire 
long term period. A general, broad steering mid level flow 
across the northern tier states will keep weather systems moving
along into early next week. Beyond that, it appears the H5 mass
fields start to amplify as a long wave trough digs across the 
western Plains states while ridging builds across eastern Canada
by around Monday night or Tuesday, though noting some solution 
spread amongst the model members. 

As high pressure heads east off the eastern seaboard, an 
approaching cold front will slide SE Friday night into early 
Saturday. Noting decent instability as it shifts into northern 
New England, but tends to break down as the front approaches the
region. Noting K indices in the lower 30s and TQ values in the 
upper teens Fri night. Have mentioned isolated thunder in the 
Fri night/early Sat forecast. However, the energy and 
instability outruns the approaching front, and actually weakens 
as it passes. 

Large high moves in behind the front through the remainder of 
the weekend into the start of the work week. Rather cool 
conditions, especially moving into Monday morning as another 
reinforcing high brings overnight lows in the lower-mid 40s 
across the higher inland terrain, ranging to the mid-upper 50s 
along the S coast. 

Another complex system approaches Monday night or Tuesday, but 
model timing with the exit of high in question, which is lending
to model solution spread. May see another round of showers and 
even a few thunderstorms, but noting only marginal instability 
with this next system. 

&&

.AVIATION /09Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

Low - less than 30 percent. 
Moderate - 30 to 60 percent.   
High - greater than 60 percent.

Short Term /through Friday/...

Through 12z...Mainly MVFR and low end VFR cigs. 

Today...Moderate confidence.
A mix of MVFR/VFR cigs becoming all VFR, but MVFR persisting
over Cape/Islands where a brief shower possible this morning. 

Tonight...Moderate confidence. 
Areas of stratus and patchy fog developing with MVFR/IFR 
conditions, mainly interior. 

Friday...Moderate confidence.
Any MVFR/IFR stratus in the interior improving to VFR by 
midday. S/SW gusts to 25 kt developing in the afternoon. 

KBOS Terminal...High confidence in trends. Lower confidence in
timing. 

KBDL Terminal...High confidence in trends. Lower confidence in
timing. 

Outlook /Friday Night through Monday/...

Friday Night: Mainly VFR, with areas MVFR possible. Windy with
gusts to 30 kt. Chance SHRA, slight chance TSRA.

Saturday: VFR. Breezy. Slight chance SHRA.

Saturday Night through Sunday Night: VFR. 

Monday: VFR. Breezy. 

&&

.MARINE...
Forecaster Confidence Levels...

Low - less than 30 percent. 
Moderate - 30 to 60 percent.   
High - greater than 60 percent.

Short Term /through Friday/...High confidence.

Today...NE winds gradually diminish, especially this afternoon 
but 5-6 ft seas will persist over eastern waters.

Tonight...Light winds as high pres builds over the waters, but 
5 ft seas continue over eastern waters.

Friday...Increasing southerly winds with gusts to 25-30 kt 
developing by late afternoon, especially eastern MA waters. 

Outlook /Friday Night through Monday/...

Friday Night: Low risk for gale force winds with gusts up to
35 kt. Seas up to 5 ft. Slight chance of rain showers, isolated
thunderstorms. 

Saturday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Areas of seas approaching 5 ft. Slight chance of rain
showers. 

Saturday Night through Sunday: Winds less than 25 kt. 

Sunday Night: Winds less than 25 kt. Seas locally approaching
5 ft. 

Monday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ250-254.
     Small Craft Advisory until 8 PM EDT this evening for ANZ251.
     Small Craft Advisory until 10 AM EDT this morning for ANZ255-
     256.

&&

$$
SYNOPSIS...KJC/EVT

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