US Extended Weather Forecast thru July 20

Short Range Forecast Discussion
Valid 12Z Sat Jul 13 2013 - 12Z Mon Jul 15 2013

...There is a slight risk of severe thunderstorms over of the Northern

...Heavy rain possible over parts of the Northern and Southern Plains...

Upper-level low over Kentucky, Southern Ohio Valley, will move westward to parts of the Southern/Central Plains by Sunday evening. The retrograding system will produce showers and thunderstorms over parts of the Tennessee Valley and the Western Ohio Valley on Saturday. The storm will produce heavier rain and thunderstorms over parts of the Southern/Central Plains on Sunday.

In addition, a plume of moisture will also move westward from the Atlantic Coast to Central Gulf Coast/Western Ohio Valley by Sunday.

Diurnal heating and orographic forcing will produce shower and
thunderstorms from the Atlantic Coast to the Eastern Gulf Coast, waning by Sunday evening.

Meanwhile, a quasi-stationary boundary over the Upper Midwest and
upper-level energy crossing the the West-Central U.S./Canadian border will trigger showers and thunderstorms over parts of the Upper Mississippi Valley/Upper Great Lakes that will expand roughly southwestward to the Central High Plains/Northern Plains by Sunday.

Additionally, weak monsoonal moisture and diurnal heating will produce showers and thunderstorms over parts of the Southwest/ Central Rockies and the Great Basin on Saturday and Sunday.
Extended Forecast Discussion
Valid 12z Tue Jul 16 2013 - 12z Sat Jul 20 2013

Ensemble 18z Gefs/12z Ecmwf Ensemble Guidance Remains In Better Than Average Agreement With Upper-Level Flow Regime.

...Southwest Us...

Another Retrograding Upper-Level Trough And Possible Embedded
Cutoff 500 Mb Low Drifts West From The Southern High Plains Into The Southwest On Thu And Fri 19 Jul.

The Steeper Lapse Rates/Upper Divergence Maxima Near The Trough Axis Coupled With An Open Gulf Moisture Tap Spells Widespread Showers/Storms In West Tx/Nm.

The Rainfall Has Potential To Make Up For The Ongoing Rainfall Deficit/Provide Partial Relief To A Drought Stricken Region.

The Latest Cpc Drought Monitor Shows Extreme To Exceptional Drought Conditions Across Nm/West Tx-Tx Panhandle. 700 Mb Temperatures Show Values 2-3 Std Deviations Below Normal In West Tx/Nm...So The Proximity Of The Closed Low Wed-Thu Also Provides Much Cooler Than Normal Temperatures.

...Pacific Northwest To Northern Rockies/Northern Great Basin...

The Persistent Upper Trough Off The Coast In The Northeast Pacific
And Possible Embedded Closed Low Leads To A Downstream Ridge Over The Pacific Northwest/Northern Great Basin/Northern Rockies. The 12z Ecmwf Forecast Closed Low Is On The Southwest Edge Of The Model/Ensemble Guidance...Which Forces The 500 Mb Ridge Axis Further West In The Pacific Northwest. The Good Agreement Amongst The 18z Gfs/18z Gefs Mean/12z Ecmwf Ensemble Mean Suggests Using The Majority Cluster. This Leads To 700 Mb Temps Of 1.5-2 Std Deviations Above Normal And Sfc Temps Commonly 5-10 Degrees Above Normal Across Interior Sections Of Wa/Or Across Id/Western Mt.

...Ms Valley/Great Lakes/Oh Valley/Northeast/Mid Atlantic...

Mid-Upper-Level Anticyclone Over The Ohio Valley To The Mid Atlantic And Mid Ms Valley Persist Through Mid Week Before Drifting South Into Tn Valley Fri-Sat As The Gradually Amplifying Trough Over Eastern Canada Builds Down Into The Us And Drives A Cold Front South Across The Lakes And Northeast On Fri 19 Jul And Then Mid Atlantic And Oh Valley On Sat 20 Jul.

For The Wed-Fri Period...The Gefs 850-700 Mb Temps Are 1-2 Std Deviations Above Normal From The Northern Plains Across The Upper Ms Valley/Oh Valley And Mid Atlantic States...Peaking In The Mid Atlantic. Temps Are Fcst To Be Several Degrees Hotter Than Normal...Then Gradually Cooling As The Front Enters The Us Fri And Continues South Sat With Upper Divergence/Lower Convergence Couplets Near The Front Triggering Scattered To Numerous Showers/Storms.

...Fl And Gulf Coast...

A Series Of Weak Low-Level Waves In The Subtropical Easterlies
Migrating Through Florida And The Northern Gulf Of Mexico Should
Bring Periods Of Showers And Embedded Thunderstorms To The Gulf Coast States. The Gefs Precipitable Water Anomalies Suggest Dry Air Wrapping Around The Mid Atlantic To Southeast Anticyclone May Bring A Period Of Decreased Shower Activity To Northeast
Fl/Adjacent Ga Wed-Thu.

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