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fxus61 kbox 121107 
afdbox 


Area forecast discussion 
National Weather Service Taunton Massachusetts 
607 am EST Friday Mar 12 2010 


Synopsis... 
onshore flow will persist with cool temperatures. Precipitation will 
spread across the southwestern half of the forecast area this 
afternoon and tonight as low pressure forms along the North Carolina 
coast. This will become a major slow moving middle Atlantic coastal 
storm over the weekend. It will produce multiple hazards with potential 
for small pockets of damage in southern New England before the storm 
departs southeast of Nantucket late Monday. Strong Great Plains high 
pressure follows...probably delivering a spell of beautiful Spring 
weather here during the middle and end of next week. 


&& 


Near term /until 6 PM this evening/... 
radar still indicating light precipitation across portions of extreme 
eastern Massachusetts early this morning. However this is expected to 
depart by daybreak as there will be some brief short wave ridging this 
morning. 


Next batch of showers is currently advancing north from the Delaware-Maryland-Virginia 
into southern New Jersey and Pennsylvania. This batch of showers 
is associated with an approaching 500 mb short wave disturbance. Also 
noting an increase in a southeasterly 850 mb jet providing more 
thermodynamic lift by this afternoon across southwestern portions of 
the forecast area. So have increasing probability of precipitation midday through the 
afternoon hours particularly across Connecticut...western 
Massachusetts and western Rhode Island. 


Due to prevailing cloud cover and onshore flow...favor the cooler 
met guidance for today. 


&& 


Short term /6 PM this evening through 6 am Saturday/... 
tonight...cool high pressure will attempt to build from the 
Canadian Maritimes into northeast portions of the forecast area. 
Meanwhile low pressure will develop along the North Carolina coast. 
Mild and moisture laden Atlantic air will attempt to overspread 
the area. 500 mb ridging and drier surface air advecting southwestward 
will attempt to keep precipitation from advancing too quickly 
northeast. However an increasing low level southeast jet and increasing 
thermodynamic lift will focus chance to likely probability of precipitation across central 
and western portions of the forecast area. 


A cool air damming signature is noted on the latest operational 
model runs. Thermal profiles are marginally cold enough to support 
a mix of sleet and freezing rain with some snow possible across 
portions of the east slopes of the Berkshires. 00z NAM/GFS indicate 
0c isotherm around a 1000 to 1500 foot level. Given some uncertainty 
regarding ptype issues...have held off on a Winter Weather Advisory 
for late tonight at this point. The 12z models may have a better 
handle on this. 


&& 


Long term /Saturday through Thursday/... 
***major storm with a variety of hazards anticipated for our area 
Saturday through midday monday*** 


The northward extent of The Hazards still has some doubt although we 
think the steady hand of the cyclic European model (ecmwf) as well as the northeastward 
progressing sref probs will prevail with additional support from the 
00z/12 ggem and UKMET...offsetting the somewhat staggering successive op 
runs of the GFS and NAM. 


In essence...not much change anticipated from previous forecast with the weekend 
storm and if anything as we draw closer the cues are no longer lessening. 


Time requires that this is kept simple... 


The hwobox has The Hazards discussion. 


Travel in coastal southeast New England will be hampered Sat night into 
Sunday...rain and wind! 


Heavy rain will occur... ranging from maybe an inch of water equiv 
precipitation in Cheshire County of SW New Hampshire to perhaps 5 inches by noon Monday 
in parts of coastal Massachusetts or Rhode Island. Any amounts over 4 
inches I think will trigger minor flooding. The question...do we 
reach that threshold...still too early to know but flooding of the 
magnitude that occurred in late Feb is still possible in eastern 
mass and Rhode Island. Snowmelt may not be very large in the hilly 
interior due to cold rains but still will be a currently unknown 
contributing runoff factor. Please note...the latest 03z sref now 
have a 25 percent probability of 4 inches in NE mass ending 18z Monday with a 36 
hour 60 percent probability of 3 inches on Boston ending 12z Monday! Its back 
and I think until we see a complete dismantling of the European model (ecmwf) 
consistency for this event...that we need to be alert for minor to 
MDT water problems in the NE mass and north Rhode Island regions Sunday into 
Monday. Both sref and gefs now have 5 South Dakota of 850 inflow on southern New England Sunday 
morning for a 6 to 15 hour period. This is going to be substantial 
water equivalent trouble. 


Wind...associated Transfer during Sat afternoon in the interior of 33 to 
38 kts but especially with pressure falls and low level jet Sunday morning Rhode Island and 
coastal Massachusetts! The signal looks strong for possible damaging 
gusts of 50 knots southeast New England coast around 03z-09z! Wind composites 
are helpful. Bl wind will be 50 to 60 knots there! Even the interior 
and North Shore will have bl wind of 30-38 knots and while not quite as 
substantial as the late Feb event...it still is a problem. Travel for 
high profile vehicles will be problematic early Sunday morning along 
the coast. 


Then the southeastward collapsing strong bl wind field Monday along the mass 
coast will support Wind Advisory conditions in the 10z-18z time frame on 
the emass coast. 


Ice and or snow...small but hazardous amount risk lurks for the high 
terrain...especially northeast facing slopes of the Berkshires...Monadnocks 
and possibly the orh hills...both Sunday and Monday mornings. No 
confidence on details but can see eventual advisory issuance. 


Coastal flooding....we increased surge based on 06z/12 departures running 
it up .5 to .7 feet above the 04z mrpsse Saturday into Monday. So far 
the results are minor episode...but I do not like the look of the 
persistent NE gales building very large energetic swells sweeping 
ashore by Sunday afternoon into Monday. 


Temperatures...used the coldest of the available 00z guidance with I think the 
European model (ecmwf) best in depicting both temperatures and dewpoints. 


Then wind forecast was blended 00z/12 NCEP MOS and GFS gust along. 




Monday night through Thursday... 


Gradual improvement with some outstanding weather anticipated here Wednesday- 
Friday. Raised temperature guidance above the GFS guidance...especially interior. 


&& 


Aviation /11z Friday through Tuesday/... 
today...moderate to high confidence MVFR ceilings 1500-2500 feet 
across the western terminals kbaf-kbdl and as far east as korh. 
Local IFR ceilings possible across the east slopes of the Berks. 
Moderate to high confidence VFR ceilings holding across the 
eastern terminals. Some possibility of MVFR visibilities 3-5 sm in 
rain showers this afternoon western terminals and kmht in patchy fog 
through 12z this morning. 


Tonight...MVFR ceilings kbdl-kbaf with scattered-numerous rain showers. Precipitation will mix 
with sleet freezing rain and some snow along the east slopes of the 
Berks by 03z. Elsewhere VFR ceilings and visibilities will prevail with 
numerous showers remaining across the southwestern half of the area. 


Outlook... 


Sat...MVFR lowering to IFR from SW to NE. NE g27-35 kts developing 
throughout. Ice possible northwest Massachusetts and southwest New Hampshire early Sat. 
Low confidence on timing of MVFR to IFR. 


Sat night...high confidence on IFR in wind driven rain. Strong east 
winds 30-40 knots eastern Massachusetts and Rhode Island along with probable low level wind shear. Ice 
possible east slopes of the Berks. 


Sun...high confidence IFR/LIFR in rain/drizzle fog...possibly 
changing to snow at night orh and other high terrain terminals. NE 
gusts bos to orh at least 27-37 knots. 


Monday...MVFR ceilings becoming VFR northwest half. MVFR ceilings and areas of rain or 
rain mixed with some wet snow southeast half with local IFR ceilings/visibility in 
the morning. Moderate confidence. NE wind gusts 30-40 knots bos to the 
cape and islands in the morning. 


Monday night...high confidence of becoming VFR. 


Tuesday...high confidence VFR. 


&& 


Marine... 
today...small craft advisories remain posted across the southern 
waters. Could see a few gusts to 25 knots as the pressure gradient wind 
increases. Have seas building to 4 to 7 feet this afternoon across 
the southern waters. Across the northern waters the Small Craft 
Advisory has been delayed until tonight. 


Tonight...small craft advisories expand into the northern waters 
with building east swell. Widespread gusts to 25 knots. 


Outlook... 
Sat-Mon...mww posted with the Gale Warning. Low probability storm force gusts 
early sun and and then again Monday morning. Bos harb and narr Bay not 
yet converted to Gale Warning due to timing uncertainty. 


Monday night-Tue...seas subside to 8 to 12 feet Monday night and to 6 to 10 feet 
over the outer waters Tuesday. Winds will finally diminish to below Small 
Craft Advisory levels by late Tuesday afternoon. 


Kept the 4pm Thursday forecast seas as they looked more accurate then the 
slightly less GFS ww vsn. No Swan guidance available at 2am. 


&& 


Hydrology... 
heavy rain will occur... ranging from maybe an inch of water equiv 
precipitation in Cheshire County of SW New Hampshire to perhaps 5 inches by noon Monday 
in parts of coastal Massachusetts or Rhode Island. Any amounts over 4 
inches I think will trigger minor flooding. The question...do we 
reach that threshold...still too early to know but flooding of the 
magnitude that occurred in late Feb is still possible in eastern 
mass and Rhode Island. Snowmelt may not be very large in the hilly 
interior due to cold rains but still will be a currently unknown 
contributing runoff factor. Please note...the latest 03z sref now 
have a 25 percent probability of 4 inches in NE mass ending 18z Monday with a 36 
hour 60 percent probability of 3 inches on Boston ending 12z Monday! Its back 
and I think until we see a complete dismantling of the European model (ecmwf) 
consistency for this event...that we need to be alert for minor to 
MDT water problems in the NE mass and north Rhode Island regions Sunday into 
Monday. Both 03z sref and 06z gefs now have 5 South Dakota of 850 inflow on southern New England 
Sunday morning for a 6 to 15 hour period. This is going to be 
substantial water equivalent trouble. 


&& 


Tides/coastal flooding... 
coastal flooding....we increased surge based on 06z/12 departures running 
it up .5 to .7 feet above the 04z mrpsse Saturday into Monday. So far 
the results are minor episode...but I do not like the look of the 
persistent NE gales building very large energetic swells sweeping 
ashore by Sunday afternoon into Monday. 


&& 


Climate... 
3/11/10 clibos has missing wind data since 1026am data of 32 
sustained and gust 76 miles per hour was incorrect. Unsure of the source. 


Also...ghg data rts today Ard 22z and but the data for 3/11 there 
will be incomplete. 


&& 


Equipment... 
etss guidance on the kbox web has not updated for 2 days...we will ck 
this during the daylight hours Friday but please do not use this. We 
are increasing surge guidance by at least half a foot through the next 4 
days due to persistent onshore flow and we should have a surge of 2 
feet or more on Sunday along the east mass coast. 


&& 


Box watches/warnings/advisories... 
CT...none. 
Massachusetts...none. 
New Hampshire...none. 
Rhode Island...none. 
Marine...Small Craft Advisory from 10 am this morning to 6 am EST 
Saturday for anz232>235-237-254>256. 
Gale Warning from 1 PM EST Saturday to 1 PM EDT Sunday for 
anz231>234-250-251-254. 
Gale watch from Saturday afternoon through Sunday morning for 
anz230-236. 
Small Craft Advisory from 7 PM this evening to 6 am EST 
Saturday for anz231-250-251. 
Gale Warning from 6 am EST Saturday to 7 am EDT Sunday for 
anz235-237-255-256. 


&& 


$$ 
Synopsis...drag/Strauss 
near term...Strauss 
short term...Strauss 
long term...drag 
aviation...drag/Strauss 
marine...drag/Strauss 
hydrology... 
tides/coastal flooding... 
climate... 
equipment... 

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