Rainy Weekend

Well, I'm not very confident about the placement of the bullseye of rain by the GFS, but someone is going to get a lot of rain this weekend as an area of low pressure forms and tracks across the Gulf coast. It appears now that the bulk of rain heavier will stay south of I-20, but everyone in Georgia may see some rain before it's all over. Most of this begins later Saturday, so if you have yard work to do, get out early if possible.

We'll start with the latest Area Forecast Discussion by the Atlanta National Weather Service Office. I bolded a few sections that I thought were important.

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... 
A SLOW MOVING LOW PRESSURE SYSTEM STILL EXPECTED TO IMPACT THE REGION SUNDAY INTO EARLY TUESDAY. AN OLD FRONTAL BOUNDARY BEGINS TO PUSH NORTH ACROSS THE NORTHERN GULF OF MEXICO AND FLORIDA PANHANDLE SATURDAY NIGHT INTO EARLY SUNDAY. A LOW PRESSURE WAVE IS EXPECTED TO DEVELOP ALONG THE OLD FRONT BY LATE SUNDAY AND SLOWLY MOVE EAST THROUGH EARLY TUESDAY BEFORE EMERGING OFF THE SE COAST. 

MODELS CURRENTLY DIFFER ON EXACTLY HOW FAR NORTH THE FRONT AND SURFACE LOW WILL PUSH... WITH PROGGED LOCATIONS ANYWHERE FROM ALONG THE I-20 CORRIDOR TO THE GA/FL LINE. THE GFS IS MUCH FURTHER SOUTH THAN THE NEW ECMWF. THE POSITIONING OF THE LOW CENTER/FRONT WILL HEAVILY INFLUENCE RAINFALL TOTALS AND THE POTENTIAL FOR THUNDER. WITH THE NORTHERN SOLUTIONS...THE HEAVIER RAINFALL/THUNDER POTENTIAL WILL BE HIGHER MAINLY ALONG AND SOUTH OF INTERSTATE 20. IF THE EVOLUTION OF THE SYSTEM IS MORE LIKE THE GFS...THEN THE HEAVIER RAINFALL AND THUNDER POTENTIAL WILL BE CLOSER TO THE GA/FL LINE. 

HAVE TAKEN A COMPROMISE. SURFACE INSTABILITY STILL LOOKS LOW...SO WILL KEEP THE CHANCES FOR THUNDER IN THE SLIGHT CHANCE/CHANCE RANGE. QPF BULLSEYES HAVE BEEN MOVING AROUND THE LAST COUPLE OF DAYS... AND MAY CONTINUE TO DO SO UNTIL A BETTER TRACK FOR THE LOW AND POSITION FOR THE BOUNDARY ARE DETERMINED. ALSO...HAVE NOTED OVERALL QPF VALUES CONTINUE TO CREEP UPWARDS. ON AVERAGE...ONE TO THREE INCHES OF RAINFALL CAN BE EXPECTED...WITH THE HIGHEST VALUES SOUTH OF THE METRO AREA. 

---

This is an excerpt of the QPF discussion by the Weather Prediction Center: 

MODELS SHOW VARIOUS LEVELS OF INTERACTION BETWEEN THE SHORTWAVE TROUGH OVER THE MIDWEST AND THE SHORTWAVE TROUGH OVER TEXAS DURING DAYS 2 AND 3. THE MAJORITY OF SOLUTIONS AGREE ON 2 DISTINCT AREAS OF RAINFALL... ONE OVER THE NORTHERN GULF COAST STATES... AND ANOTHER AREA ALONG THE CENTRAL GULF COAST PERHAPS EVEN OFFSHORE. 

 GIVEN THE COMPLEXITY OF THIS INTERACTION ALONG WITH ANY TROPICAL AND/OR HYBRID LOW DEVELOPMENT OVER THE NORTHERN GULF WHICH SOME SOLUTIONS SHOW AND ASSOCIATED HIGH SOLUTION SPREAD... THE FORECAST LEANS HEAVILY TOWARD THE ENSEMBLE MEANS DUE TO LOW CONFIDENCE. SOME DETERMINISTIC DETAIL WAS INCLUDED ON DAY 2...AND EVEN LESS ON DAY 3 AS THE SPREAD GROWS. 

THE NAM/GFS/UKMET ARE STRONGEST WITH LOW DEVELOPMENT WITH SOME SOLUTIONS PULLING THE LOW TOWARD THE SOUTHERN APPALACHIANS BY DAY 3... WHILE THE ECMWF AND SOME OTHER SOLUTIONS ARE QUITE WEAK AND KEEP THE LOW OVER THE GULF. THE CURRENT FORECAST ASSUMES A LOWER LEVEL CONVERGENCE ZONE WILL INTERCEPT THE BULK OF MOISTURE AND INSTABILITY NEAR OR JUST OFFSHORE OF THE CENTRAL GULF COAST WITH SOME LOCATIONS POSSIBLY RECEIVING SEVERAL INCHES OF RAINFALL...BUT WITH CONFIDENCE THAT IS TOO LOW TO REPRESENT WITH A SLIGHT RISK OF EXCESSIVE RAINFALL AT THIS TIME.

Listening to them, they favor more coastal to offshore development. The GFS paints the bullseye somewhere toward central Georgia as you can see in this image.

Total Precip through 2pm Monday

The WPC has their own thoughts about this system as you can see in this image:

WPC 5 day precip forecast

There will be some very high precipitable water values this weekend, upwards of 2.2". Notice how the NW corner of Georgia is missing out.

Precipitable Water Values