December 2016- End Of Year Forecast

General Weather Discussions and Analysis

Re: December 2016- Cold/Rainy Weekend. Tracking Arctic Air

Postby Electric Lizard » Wed Nov 30, 2016 7:38 am

This morning's NWS disco gets on board with next week's cold by suggesting a bear watch may be warranted soon.
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Re: December 2016- Cold/Rainy Weekend. Tracking Arctic Air

Postby srainhoutx » Wed Nov 30, 2016 8:33 am

Wednesday morning briefing from Jeff:

Wet weekend for much of the state

Same cold front responsible for the 23 tornadoes overnight in LA, MS, AL of which one struck a 24-hr daycare at 213am this morning completely destroying the structure and critically injuring four children and resulting in 3 nearby fatalities, has pushed off the TX coast allowing a refreshingly dry air mass to overspread the region.

Cold air advection will continue today with temperatures slowly falling this morning into the 50’s across much of the entire area under N winds and a mid level cloud deck. Highs will only reach the mid to upper 60’s today compared to the record breaking mid 80’s on Tuesday. Coldest morning will be Thursday under clear skies and light winds and expect temperatures to fall into the upper 30’s NW to near 50 at the coast.

Friday-Sunday:
While there are still timing differences on when this weekend storm event will begin and end…models remain in good agreement that a very wet pattern will develop over SE TX.

Friday:
An upper level storm system will move from the NW US southward into NW MX and begin to cut off from the main jet stream flow aloft. The deep southern position of the upper level trough will begin to force surface pressure falls along the lower TX coast late Friday. Moisture will rapidly return across TX from both the Pacific and the Gulf of Mexico starting on Friday and we may begin to see showers break out by late Friday afternoon…which is a little faster than the previous thinking. Developing coastal low off the lower TX coast will lock in cold NE surface winds and cold air mass over the region with mid level moisture spreading northward over this surface cold dome.

Weekend:
SW flow aloft on the eastern flank of the NW MX upper level storm system and developed/NE tracking costal trough/low will result in messy conditions for the weekend. Strong overrunning of warm moist air above the surface cold layer will result in widespread rainfall from Saturday morning well into Sunday night and likely into Monday. Rainfall, clouds, and NE wind draining cold air in to the region will keep a near steady temperature through the entire period in the upper 40’s to mid 50’s.

Current thinking is that the coastal trough/low will progress from the lower TX coast late Saturday NE/ENE to off the upper TX coast by early Monday which will bring some marine impacts to winds and possibly tides. This track of the surface features and warm/cold sectors of the storm system favors the maximum rainfall totals to be along the coast and offshore as well as any severe weather threat. Should the surface low track inland or closer to the coast higher rainfall totals and severe weather would need to be added likely for Sunday.

Rainfall Amounts:
Widespread rainfall amounts of 2-4 inches are likely over the next 5 days with most of this falling Saturday and Sunday. Expect the 2 inch totals more inland with the higher totals near the coast and offshore. Could see isolated amounts upwards of 6-7 inches over the coastal waters given forecasted PWS of 1.7-1.9 inches. Certainly the threat for heavy rainfall is there with those kind of PWS values, but current thinking is that the most concentrated convection will remain along and SE of US 59. Should the coastal trough track closer to the coast or slightly inland then rainfall amounts will need to be increased along and S of the US 59 corridor.

5-Day Forecasted Rainfall Amounts:
11302016 Jeff 1 untitled.png


Cold Air Outbreak:
Bitter cold air mass which has been stuck in Russia and Siberia for much of November has built into Alaska over Thanksgiving where current temperature readings are in the -30F to -40F range. Both the ECWMF and GFS along with several of their ensemble members develop an increasingly amplified upper air pattern next week over the northern Pacific which forces high pressure to build northward toward Alaska and then a deep downstream trough to form over the western US. This is certainly an upper level pattern favorable for delivery of a cold source region (Alaska) arctic air mass southward into the US. Given that the source region is actually fairly cold and expected to remain cold adds support to a significant intrusion of cold air into the plains by the middle to end of next week.
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Re: December 2016- Cold/Rainy Weekend. Tracking Arctic Air

Postby srainhoutx » Wed Nov 30, 2016 9:35 am

Some have been asking what the mid December toward Christmas timeframe may offer. The Updated CFSv2 Monthly climate model suggests colder than normal temperatures and slightly above normal precipitation chances. Typically I have noticed a bit of a warm bias for this particular Long Range Ensemble Model over the years. That said look how cold our source Regions of Eastern Alaska and NW Canada throughout the month.
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11302016 CFSv2_NaT2m_20161130_201612.gif
11302016 CFSv2_NaPrec_20161130_201612.gif
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Re: December 2016- Cold/Rainy Weekend. Tracking Arctic Air

Postby srainhoutx » Wed Nov 30, 2016 12:25 pm

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM EST WED NOV 30 2016

VALID 12Z SAT DEC 03 2016 - 12Z WED DEC 07 2016


...OVERVIEW...

ONCE AGAIN...THE MEDIUM RANGE PERIOD (SATURDAY THROUGH WEDNESDAY)
CONTINUES TO BE PLAGUED BY THE UNCERTAINTY OF THE UPPER TROUGH
EJECTING EASTWARD FROM NORTHERN MEXICO. HOWEVER...ENSEMBLES ARE
BEGINNING TO COME TO A CONSENSUS REGARDING ITS EVOLUTION. BY DAYS
6 AND 7...THERE CONTINUES TO BE AGREEMENT AMONGST THE MODELS WITH
THE INCOMING DIGGING TROUGH FROM THE PACIFIC.


...MODEL EVALUATION/PREFERENCES...

THE BIGGEST CHALLENGE IN THE FORECAST ONCE AGAIN IS THE TRACK AND
SPEED OF THE UPPER LOW OVER NORTHERN MEXICO ON SATURDAY. THE GFS
CONTINUES TO HAVE GOOD CONTINUITY WHILE THE 00Z ECMWF BEGAN TO
MIRROR THE OLDER MODEL RUNS OF BEING TOO FAST ALONG WITH THE
ENERGY FROM THE NORTHERN STREAM STACKING ON TOP OF THE CLOSED LOW
OVER MEXICO. THE 00Z GFS AND GEFS BOTH SHOW THE NORTHERN STREAM
QUICKLY PROGRESSING TOWARD THE EASTERN US AS THE UPPER LOW OVER
MEXICO SLOWLY TREKS TOWARD TEXAS OVER THE WEEKEND. HOWEVER...THE
ECMWF ENSEMBLE MEAN BEGAN TRENDING TOWARD THE GFS/GEFS SOLUTION
WITH THE PLACEMENT AND TIMING OF THE UPPER LEVEL LOW AND BY
MONDAY...THE UPPER LOW WEAKENS OVER TEXAS AND TRACKS EASTWARD.
BECAUSE OF THIS...USED A 00Z GEFS/GFS/ECENS BLEND BUT LEFT THE 00Z
ECMWF OUT DUE TO IT REGRESSING BACK TO ITS OLDER TRENDS.

BY DAYS 5 THROUGH 7...GOOD AGREEMENT REMAINS ON THE ENSEMBLES
SHOWING A RIDGE BUILDING ACROSS THE GULF OF ALASKA...WHICH WILL IN
TURN ASSIST IN ANOTHER UPPER TROUGH DIGGING ACROSS THE WESTERN US.
THIS UPPER TROUGH WILL PROGRESSES QUICKLY ACROSS THE CENTRAL US
BY THE END OF THE MEDIUM RANGE PERIOD. MEANWHILE...THE RIDGE WILL
BUILD BACK ACROSS THE WESTERN CARIBBEAN AND SOUTHEAST.


...WEATHER HIGHLIGHTS/THREATS...

THE POTENTIAL FOR HEAVY RAIN ACROSS THE EASTERN HALF OF TEXAS AND
THE LOWER MISSISSIPPI VALLEY REMAINS FOR THIS WEEKEND AS THE UPPER
LOW MOVES OVER THE REGION.
AT THE SURFACE...A LOW WILL TRACK
ACROSS THE WESTERN GULF OF MEXICO AND MOVE NORTHWARD ACROSS THE MS
VALLEY. IN ADDITION...VALLEY RAIN AND MOUNTAIN SNOW WILL SPREAD
ACROSS THE PACIFIC NORTHWEST AS A SURFACE FRONT MOVES ACROSS THE
AREA. SNOW WILL CONTINUE ACROSS THIS REGION IN ADDITION TO THE
NORTHERN ROCKIES AS MOIST ONSHORE FLOW CONTINUES UNDER A STRONG
WEST-EAST UPPER LEVEL JET.


EXPECT BELOW AVERAGE TEMPERATURES FOLLOWING NEAR THE CLOSED LOW IN
THE SOUTHWEST/FOUR CORNERS REGION FRIDAY INTO THE SOUTHERN PLAINS
AND SOUTHEAST THIS WEEKEND. AS THE CANADIAN HIGH SPILLS OVER THE
INTERMOUNTAIN WEST BY DAY 6...MUCH COOLER TEMPERATURES WILL FILTER
ACROSS THE WESTERN US...WITH TEMPS 15-25F BELOW THE AVERAGE.
THE
EAST WILL SEE A WARMING TREND AS THE UPPER RIDGE BUILDS IN FROM
THE SOUTHEAST.


FANNING


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11302016 12 GFS 138 gfs_apcpn_scus_23.png
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Re: December 2016- Cold/Rainy Weekend. Tracking Arctic Air

Postby srainhoutx » Wed Nov 30, 2016 1:48 pm

11302016 Mike Ventrice Cyh7O1OWIAAXKeK.jpg

Michael Ventrice ‏@MJVentrice · 21m21 minutes ago  Andover, MA
Big cut-off low to impact the South this weekend could produce some very heavy rains across Texas; Newest ECMWF putting out 3-6" thru Monday

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Re: December 2016- Cold/Rainy Weekend. Tracking Arctic Air

Postby DoctorMu » Wed Nov 30, 2016 3:06 pm

Bullseye on Galveston for the weekend rain.

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Re: December 2016- Cold/Rainy Weekend. Tracking Arctic Air

Postby srainhoutx » Wed Nov 30, 2016 3:45 pm

The afternoon Updated Climate Prediction Center Outlooks for Day 6 to 10 and Day 8 to 14 suggest below normal temperatures will spread across the United States.
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Re: December 2016- Cold/Rainy Weekend. Tracking Arctic Air

Postby jasons » Wed Nov 30, 2016 7:07 pm

Euro and GFS sure look different on rainfall placement.
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Re: December 2016- Cold/Rainy Weekend. Tracking Arctic Air

Postby srainhoutx » Thu Dec 01, 2016 4:22 am

The overnight updated quantitative precipitation forecast and the excessive rainfall outlook suggest we may have some issues across the Eastern half of Texas extending into Louisiana.
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Re: December 2016- Cold/Rainy Weekend. Tracking Arctic Air

Postby unome » Thu Dec 01, 2016 6:00 am

srainhoutx wrote:The overnight updated quantitative precipitation forecast and the excessive rainfall outlook suggest we may have some issues across the Eastern half of Texas extending into Louisiana.

the very soggy day 3

the closed mid level moves slowly east to western mexico during day 3. the low level inflow increases to about 30 knots from the southwest... continuing to funnel 1.75/2.00 inch preciptable water air across eastern tx into portions of la. while there is some spread on the placement of a frontal boundary extending from low pressure over far south tx... the low level moisture and marginal to locally moderate instability becomes focused on the front... increasing the threat for heavy to excessive rainfall. an axis of 2.75 to 3.50 inches of qpf was stretched from the middle tx coast across northern la and far southern ar... where the best instability is expected.

these qpf amounts are lower than the maximum qpf amounts from the 00z gfs (and even the 00z ecmwf). locally higher amounts are possible... as corfidi vectors become better aligned with the mean 850-300 mb flow ahead of the closed mid level system. members of the 00z gefs and 12z ecmwf ensemble output suggest that potential for 4.00+ inch qpf amounts... mainly over the upper tx coast into northern la. three hour flash flood guidance values are generally 2.50 to 3.50 inches... and given some of the qpf amounts from the 00z model suite... as well as the potential for training in a high moisture content airmass... a slight risk area was placed over much of eastern tx... the eastern half of la and southernmost ar for day 3.


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