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January 3-4, 2015 Storm Obs/Nowcast


Baroclinic Zone

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BOX 4pm discussion.

000

FXUS61 KBOX 032109

AFDBOX

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE TAUNTON MA

409 PM EST SAT JAN 3 2015

.SYNOPSIS...

APPROACHING LOW PRESSURE WILL CONTINUE TO SPREAD A WINTRY MIX OF

PRECIPITATION INTO SOUTHERN NEW ENGLAND THIS EVENING. THE

PRECIPITATION WILL CHANGE TO ALL RAIN TONIGHT INTO SUNDAY

MORNING. THE LOW WILL TRACK INTO THE ST LAWRENCE RIVER VALLEY

SUNDAY...BRINGING MILD BUT SHOWERY WEATHER TO THE REGION. THE

TRAILING COLD FRONT WILL BRING MORE SHOWERS SUNDAY AFTERNOON AND

EVENING FOLLOWED BY DRIER BUT MUCH COLDER WEATHER MONDAY. A PERIOD

OF SNOW SHOWERS ARE POSSIBLE TUESDAY AND TUESDAY NIGHT...FOLLOWED

BY BITTERLY COLD WEATHER FOR THE REMAINDER OF THE WEEK.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...

400 PM UPDATE...

DIGGING SHORTWAVE IN THE SOUTHERN PLAINS PER WATER VAPOR IMAGERY

WILL PUSH SOUTHERN STREAM SURFACE LOW TOWARDS THE ST. LAWRENCE

VALLEY BY TOMORROW AFTERNOON. A SECONDARY LOW PRESSURE SYSTEM LOOKS

TO DEVELOP ACROSS SOUTHERN NEW ENGLAND TONIGHT. THIS WEAK SURFACE

LOW WILL BE THE MAIN FOCUS ON THE WEATHER FOR TONIGHT.

CURRENTLY INITIAL PRECIP HAS STARTED TO EXPAND ACROSS MOST OF

SOUTHERN NEW ENGLAND. BECAUSE OF WET-BULBING...THE INITIAL PRECIP HAS

FALLEN AS SNOW. IN FACT SEVERAL OBS AND WEBCAMS SHOW SNOW STICKING

ACROSS CONNECTICUT. EXPECT THIS SNOW FALL TO EXPAND INTO MASS AND

RHODE ISLAND. A QUICK INCH OR TWO IS EXPECTED AS EASTERLY FLOW OFF

THE OCEAN WILL ALLOW FOR THE PROFILE TO MOISTEN UP.

FOR THE REMAINDER OF THE AFTERNOON EXPECT SNOW TO EXPAND ACROSS THE

REMAINDER OF SOUTHERN NEW ENGLAND AND STICK TO THE SURFACES AS THE

GROUND TEMPERATURES ARE BELOW 32F. EXPECT THE HIGHER TERRAIN TO SEE

THE BEST CHANCE OF 2 INCHES OR HIGHER IN SNOW TOTAL. OTHERWISE ALONG

THE COASTLINES COULD SEE A QUICK BURST OF SNOW THEN A MIX OF

SNOW/SLEET DURING THE LATE AFTERNOON.

TONIGHT...

12Z GUIDANCE IS IN EXCELLENT AGREEMENT IN SHOWING AN 800-850MB 2-4C

WARM NOISE PUSHING INTO SOUTHERN NEW ENGLAND AFTER 00Z. IN FACT

BETWEEN 00Z AND 06Z SOME GUIDANCE JUMPS 850MB TEMPS FROM 0C TO 7C.

THIS WILL ALLOW FOR A QUICK CHANGEOVER FROM SNOW TO SLEET SOUTHWEST

TO NORTHEAST THIS EVENING. THE TRANSITION WILL BE VERY QUICK ALONG

COASTAL REGIONS AS WELL AS ALONG THE I-95 CORRIDOR. IF TEMPS LINGER

AROUND FREEZING DURING THIS TRANSITION...A PERIOD OF FREEZING RAIN

MAY BE POSSIBLE ALLOWING FOR A TRACE OF ICE YIELDING TO SLICK TRAVEL

CONDITIONS THIS EVENING. THEREFORE HAVE NOT MADE ANY CHANGES TO THE

WINTER WEATHER HEADLINES.

BIGGEST CONCERN FOR THIS PERIOD HOWEVER IS THE POTENTIAL FOR ICE

ACCRETION ACROSS THE INTERIOR. AS MENTIONED BEFORE...A GOOD WARM

LAYER WILL MOVE INTO SOUTHERN NEW ENGLAND. THIS WILL ALLOW FOR SNOW

TO TRANSITION TO SLEET THEN TO FREEZING RAIN. BIGGEST CONCERN IS

ACROSS THE CONNECTICUT VALLEY REGION WHERE SHALLOW COLD AIR WILL

REMAIN TRAPPED THANKS TO MARITIME HIGH PRESSURE AND WEAK LOW MOVING

ACROSS SOUTHERN NEW ENGLAND. WITH TEMPS BELOW 32F AND STRONG WARM

LAYER ALOFT...ANTICIPATE ABOUT 0.15-0.35 INCH OF ICE

ACCRETION...WITH HIGHER AMOUNTS POSSIBLE. THIS MUCH ICE WILL MAKE

TRAVEL DIFFICULT AND COULD ALSO RESULT IN A FEW POWER OUTAGES AND

DOWN LIMBS. LUCKILY THE WINDS WILL BE RELATIVELY LIGHT SO WIDESPREAD

POWER OUTAGES ARE NOT ANTICIPATE. GUIDANCE ALWAYS TRIES TO SCOURING

THE TEMPS OUT TOO FAST FOR THIS REGION SO LINGERED SHALLOW COLD AIR

A LITTLE LONGER THEN WHAT MODELS ADVERTISE. BELIEVE THAT AREAS IN

THE WINTER STORM WARNING HAVE THE BEST CHANCE TO SEE A FEW POWER

OUTAGES AND THE HIGHER ICE ACCRETION...SO WILL CONTINUE THE WARNING.

LASTLY...AS THE SURFACE LOW DEVELOPS AND PASSES OVER SOUTHERN NEW

ENGLAND AND WARM AIR ALOFT SURGES NORTHWARD...A MODEST LLJ OF 50-60

KTS WILL DEVELOP OVER THE CAPE. HOWEVER BECAUSE IT IS A SOUTHERLY

JET IS WILL STRUGGLE TO MIX FULLY DOWN. HOWEVER COULD STILL SEE SOME

ISOLATED GUSTS NEAR 45 MPH ACROSS THE CAPE TONIGHT.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...

TOMORROW...

MAIN SURFACE LOW OVER THE GREAT LAKES WILL PUSH INTO THE ST LAWRENCE

VALLEY TOMORROW. THIS WILL ALLOW FOR THE REMINDER OF THE COLUMN TO

WARM ABOVE 32F SO THE POTENTIAL FOR FREEZING RAIN ACROSS THE

INTERIOR WILL COME TO AN END. THE FOCUS THEN TRANSITIONS TO THE RAIN

AND WIND POTENTIAL.

SOUTHERN NEW ENGLAND WILL BE ON THE WARM SIDE OF THIS ANOMALOUS

SYSTEM WITH PWATS NEAR 3 TO 4 STAND DEVIATIONS AWAY AND 850 MB WINDS

ALSO 2 TO 3 STAND DEVIATIONS AWAY.

FOCUSING ON THE WINDS...LLJ WILL BE MORE OUT OF THE SW AT 925 MB

STREAMING BETWEEN 50-70 KTS. HOWEVER IT IS HARD TO MIX DOWN AT A

SOUTHERLY WIND AND MANY SOUNDINGS DO SHOW AN INVERSION THROUGHOUT

THE DAY. YET IT APPEARS THAT WE COULD HAVE HEAVY RAINFALL SO WITHIN

ANY HEAVY SHOWER MAY AID FOR THE STRONG WINDS TO MIX DOWN TO THE

SURFACE. THEREFORE WILL CONTINUE WITH THE WIND ADVISORY FOR THE CAPE

AND ISLANDS WHICH HAVE THE BEST CHANCE OF MIXING.

HEAVY RAINFALL IS A POTENTIAL AS THE LOW PRESSURE SYSTEMS COLD FRONT

BEGINS TO PUSH ACROSS THE REGION TOMORROW. THIS YIELDS TO PWATS

CLOSE TO AN 1.5 INCHES...ESP ACROSS THE SOUTH COAST. EVEN SOME OF

THE HI-RES GUIDANCE SHOWERS A POTENTIAL FOR SOME RAIN BANDS TO

DEVELOP AND TREK ACROSS SOUTHERN NEW ENGLAND...WHICH MAY YIELD TO

MINOR URBAN FLOODING THANKS TO A HIGH AMOUNT OF MOISTURE IN THE

ATMOSPHERE. ISOLATED THUNDER IS ALSO POSSIBLE AS SURFACE LI`S DROP

BELOW 0. ANY CONVECTION THAT DOES DEVELOP WILL ALSO YIELD TO A RISK

OF TRAINING AND URBAN FLOODING. THE BEST REGION FOR THIS TO OCCUR IS

ACROSS THE SOUTH COAST OF MA AND RI.

FINALLY SURFACE TEMPS WILL WARM THROUGHOUT THE DAY WITH PERHAPS A

FEW SPOTS HITTING CLOSE TO 60F. IF THAT DOES OCCUR THEN WE MAY MIX

OUT ALLOWING FOR WINDS TO GUST HIGHER AT THE SURFACE.

Good write up. As some thought, ice could be a bigger issue.
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