Sat Dec 21 Convective Outlook
Mdt Risk Of Svr Tstms for parts of Lwr Ms And Lwr Tn Vlys...
Slgt Risk Of Svr Tstms Surrounding The Mdt Risk Area...
from E Tx & the Cntrl Gulf Cst Ne into the Oh Vly...
An Outbreak Of Svr Tstms Is Possible Today Into Tngt Over The Lwr Ms and Lwr Tn Vlys. The Potential Will Exist For A Few Strong
Tornadoes...In Addition To Swaths Of Dmgg Winds.
Potent Shortwave Trough Now Entering W Tx Should Pivot Ne Across The Red Rvr Vly Later Today/Early Tngt...And Accelerate Ne Into Il Early
Sun...As Large-Scale/High-Amplitude Trough Remains Centered Over The Plains. The Shortwave Will Assume A Slightly Negative Tilt Before It Becomes Absorbed Within Downstream Confluent Flow Over The Oh Vly Later Sun.
Ahead Of The Impulse...Strengthening/Deepening Swly Flow Will Allow A Swath Of Seasonably Warm/Moist Air To Surge Ne Across The Lwr Ms Vly Into Much Of The Oh Vly Today Through Early Sun.
Coupled With The Very Strong Wind Field Accompanying The Upr Impulse...Setup Will Be Favorable For Bands Of Tstms/Supercells Capable Of Both Dmgg Wind And Potentially Strong Tornadoes Later Today Into Tngt.
Wrn/Cntrl Gulf Cst Into The Oh Vly Today/Tngt...
Sfc Obs Show Strong/Broad Current Of Very Moist Air Surging N From
The Wrn Gulf Of Mexico Attm Into The Lwr Ms Vly...Ahead Of Slowly Progressive Cold Front Associated With W Tx Shortwave Trough.
Numerous Buoys Report 30 Kt Sly Flow With Dewpoints Aoa 70 F In Area With Pw Aoa 1.50 Inches. The Moist Plume Will Spread Farther Ne Across The Oh Vly Through Early Sun...And Largely Delineate The Nrn/Ern Extent Of Sfc-Based Instability Across The Region.
Clouds Will Limit Diurnal Steepening Of Low-Lvl Lapse Rates Over Most Areas. But Quality Of Moisture Inflow And Presence Of Residual Eml Likely Will Yield Sufficient Buoyancy /Mlcape Of 500-1000 J Per Kg/ For Sustained Tstms...Especially Over The Lwr Ms Vly/Deep South.
Widespread Showers/Storms Now Occurring Along And W Of The Cold Front Should Gradually Increase In Strength/Coverage Through Later This Morning As Stronger Forcing For Ascent Associated With The Upr Impulse Approaches The Warm Sector. Together With Continued Moistening Of Confluent Lwr Tropospheric Flow...Setup Also May Support Development Of Bands/Clusters Of Storms Ahead Of The Front Over Far E Tx...La...Ern Ar...And Ms By Early Aftn.
Although The Intensity And Negative-Tilt Nature Of The Shortwave
Impulse May Result In Wind Profiles With A Slight Veer-Back Pattern
In The Vertical...Strength Of The Wind Field /With 60-70 Kt 850-700
Mb Winds Beneath 100 Kt Flow At 250 Mb/ Will Be Very Favorable For
The Greatest Risk For Discrete Or Semi-Discrete Storms With Potential For Tornadoes /Some Of Which Could Be Strong/...Should Exist Over Parts Of La...Ar...Ms...And Wrn Tn This Aftn/Early Tngt.
Continued Ne Motion Of The Shortwave Impulse Should Foster
Consolidation Of The Frontal And Pre-Frontal Storms Into A Fairly
Lengthy Sqln By Mid-Late Aftn.
Attendant Fast-Moving Bow/Lewp Structures Will Maintain A Risk For Swaths Of Dmgg Wind...In Addition To A Few Tornadoes...Into The Night From Wrn/Cntrl Ky Ssw Through Tn Into Ms...Al...And La.
In Addition...Although Buoyancy Will Decrease With Newd Extent...The Strongest Low-Lvl Mass Convergence/Waa Will Focus On The Oh Vly By Late Eve.
Coupled With The Intensity Of The Wind Field...And The Likelihood For Modest Sfc Development Along That Part Of The Frontal Zone Straddling The Oh Vly...Isold Tornadoes And Dmgg Wind Gusts May Occur As Far N As Parts Of Ind...Oh...And Wv Through Sun Morning.
Sun Dec 22 Convective Outlook
No Svr Tstm Areas Forecast...
A Lead Shortwave Upper Trough Will Continue To Deamplify With Newd Progression Across The Great Lakes.
A Belt Of Strong Deep-Layer Swly Flow Will Be Maintained From The Gulf Coast To The Northeast...As An Upstream Upper Trough Digs Sewd Into The Nrn Plains And Upper Ms Valley.
At The Sfc...A Weak Cyclone Will Quickly Shift Nwd Into Srn Canada By Late Morning. An Attendant Cold Front Will Slowly Progress Ewd Across The Upper Oh Valley...Appalachians...And Mid-South...Before Accelerating Late In The Period As The Cntrl Conus Upper Trough Slowly Becomes More Progressive.
Coastal Al And Fl Panhandle Newd Into The Srn Appalachians...
A Convective Line /Perhaps Not Completely Continuous/ Will Likely Be
Slowly Advancing Ewd Across The Area At The Start Of The Period.
The Shortwave Upper Trough Initially Associated With This Activity Will
Be Positioned Well To The N...With Weakening Upper Forcing For
Ascent And Low-Level Convergence Lending Some Uncertainty To How Well Organized The Line Will Be.
However...Low-Level Winds Will Initially Be Quite Strong Along The Srn Periphery Of A 50+ Kt Llj Extending Into The Lower Great Lakes... And Could Support The Potential For A Few Strong-Svr Wind Gusts And Possibly A Tornado Sun Morning.
Low-Level Flow Will Weaken Later In The Morning And Afternoon As The Llj Becomes Focused N/E Of The Area...With The Decelerating Line/Broken Line Of Convection Eventually Posing A Primary Threat For Heavy Rain...Though Isolated Strong Wind Gusts Could Still Occur.
Given The Small Temporal Window For Peak Svr Potential... Combined With The Limitations/Uncertainties Described Above...Only A 5 Percent Probabilistic Area Will Be Maintained Attm.
Carolinas And Mid-Atlantic...
Some Semblance Of A Low-Topped Convective Line Emanating Out Of The Appalachians Will Progress Ewd During The Late Morning And Afternoon Into The Va/Nc Piedmont And Across Nrn Va/Md.
The Environment Will Be Characterized By High Vertical Shear /In The Presence Of A 50+ Kt Llj/ And A Moist Boundary Layer...But Instability Will Be Limited By Poor Midlevel Lapse Rates /Despite Modest Diurnal Heating/.
Unfavorable Timing Of A Speed Max Passing N/W Of The Area Prior To Peak Heating...And Relatively Homogeneous Low-Level Wind
Fields...Yield Uncertainty To How Widespread/Organized Convective
Showers/Tstms May Be.
However...The Potential For A Few Strong-Svr Wind Gusts May Exist During The Late Morning And Afternoon.
Upper Oh Valley Into The Cntrl Appalachians...
A Weak Sfc Low Associated With An Approaching Upper-Level Speed Max Will Likely Be Positioned Across Oh Early Sun Morning...With A Plume Of Upper 50s To Perhaps Low 60s F Dewpoints Already In Place Across The Region.
A Decaying Line Of Low-Topped Showers/Tstms Moving Ewd May Pose A Risk For A Few Strong Wind Gusts Early In The Period Given Very Strong Low-/Midlevel Wind Fields...Coinciding With A Brief Window For Near-Sfc Based Parcels May Exist.
Potential Will Be Limited By Meager Instability And Early Passage Of The Speed Max W Of The Area.
Mon Dec 23 Convective Outlook
No Svr Tstm Areas Forecast...
An Upper Trough Initially Over The Middle Of The Nation Will Slowly
Become More Progressive This Period And Advance Ewd Towards The Lower Great Lakes/Cntrl Appalachians...As An Upstream Shortwave Trough Enters The Pac Nw And Nrn Rockies.
Very Strong Deep-Layer Swly Flow Will Persist On The Ern Periphery Of The Trough Through Much Of The Ern Conus.
A Sfc Cold Front Will Reach The Atlantic Coast Late Mon Evening.
Sfc High Pressure Will Become Dominant Across The Plains/Ms Valley With A Much Drier And More Stable Air Mass Encompassing Most Of The Conus...Resulting In Decreasing Convective Potential During The Latter Half Of The Period.
Coastal Plain Of Sern Va/Carolinas/Ga...
A Cold Front Will Slowly Move Ewd Towards The Sern Atlantic Coast
Through The Afternoon.
Despite Modest Midlevel Lapse Rates...Temperatures Heating Into The 70s F Should Yield Mlcape Values Of Around 200-400 J/Kg. Low-Level Frontal Convergence And Weak Midlevel Height Falls Ahead Of The Aforementioned Upper Trough Will Be Supportive For Shower/Tstm Development During The Afternoon.
With Around 35 Kt Of Mean 0-3 Km Layer Flow Present...A Few Strong
Wind Gusts May Accompany The More Robust Convection...But This
Threat Is Expected To Be Limited By Meager Instability...Precluding
Introduction Of 5 Percent Probabilities Attm.
Dec 24-28 Convective Outlook
A Seasonably Cold Air Mass Will Likely Encompass Much Of The Ern
Half Of The Conus By Tue/D4...With Sfc High Pressure Centered Near
The Oh Valley/Great Lakes.
Meanwhile...A Progressive Pattern Will Develop As A Series Of Shortwave Troughs Advance Sewd Out Of Wrn Canada.
Moisture Return Ahead Of Each Individual Trough Will Be Relatively Limited With Nly Winds Over Most Of The Nrn Gulf...Reinforced By Multiple Frontal Passages Occurring Across The Interior Conus.
As A Result...Both Instability And Svr Potential Appear To Be Minimal Through The Entire Period.