Saturday Morning Forecast

Forecast issued by Justin Gibbs on 09/16/06 at 2:00:35 am CDT

Mobile, Alabama 5 Day Forecast
Today	Sunday	Monday	Tuesday	Wednesday
91°F	90°F	88°F	85°F	84°F
	67°F	69°F	67°F	66°F
Var 4-8 mph	SE 4-8 mph	S 10-15 mph	WSW 5-10 mph	Lgt & Var
0%	30%	60%	50%	10%

Mobile, Alabama 5 Day Detailed Forecast

Today... Mostly sunny. High 91. Winds variable 4-8 mph. Tonight... Mostly clear. Low 67. Winds southeast 2-4 mph. Chance of rain is 20 percent. Sunday... Increasing clouds with scattered showers and thunderstorms. High 90. Winds southeast 4-8 mph. Chance of rain is 30 percent. Sunday Night... Mostly cloudy with isolated showers and thunderstorms. Low 69. Winds southeast 5-10 mph. Chance of rain is 20 percent. Monday... Partly cloudy with showers and thunderstorms likely. High 88. Winds south 10-15 mph. Chance of rain is 60 percent. Monday Night... Mostly cloudy with showers and thunderstorms likely. Low 67. Winds south 10-15 mph. Chance of rain is 60 percent. Tuesday... Mostly sunny with scattered showers and thunderstorms. High 85. Winds west-southwest 5-10 mph. Chance of rain is 50 percent. Tuesday Night... Mostly clear. Low 66. Winds west-northwest 5-10 mph. Wednesday... Mostly sunny. High 84. Winds light and variable.

Technical Discussion

Synopsis: 05z Surface analysis reveals a very weak ridge has built in just to our west roughly centered from KMCB/KMEI/KGTR. The influence of this ridge has calmed our winds at most stations across the area. Very dry airmass remains in place as evidenced by WV imagery and KLIX/KTLH soundings which show PWATs at 1.5 and 1.4 with strong subsidence evident from both soundings. That has led to a nearly classic environment for the radiational cooling that is occuring tonight. Aloft as would be expected analysis reveals strong ridging with the axis at 3/500mb roughly located from MSY to ORD. Downstream, however, tells a much different story as a powerful upper level low sits over the NW CONUS which has led to rapid sfc cyclogenesis over the central CONUS tonight. 850/700mb analysis indicates the airmass over the central US is being rapidly modified as the sphere of the cyclones influence increases...with SE'ly winds being reported this morning as far east as Memphis, TN. " "Forecast Discussion (Saturday through Wednesday): Short Term... Saturday is appears for now the ridging at the sfc and aloft will remain in control of the weather pattern. Little overall change from what we saw today is expected at this time with GFS/NAM forecast soundings both showing little modification of the airmass and moisture fields present. However, the column depth will be slightly greater as the upper level ridge axis moves overhead so will bump the high up 1 degree to come in line with latest MOS, which is 1 degree above Friday's high and appears rather appropriate. Saturday evening should be similar to Friday evening except we will then begin to see the slow transition to the more active pattern as the winds likely will begin to pick up from the southeast in advance of the sfc cyclone overnight Saturday. By Sunday GFS/NAM both project the upper level storm system will have opened and given way to a secondary shortwave which will amplify and push eastward. GFS/NAM are also in excellent agreement developing a secondary 300/500mb jet streak south of the main trof which then phases late Sunday and early Monday over the Mid MS VLY. This phasing will enhance divergence tremendously in the area and the placement of the vort max along the main longwave trof, and it appears appropriate for secondary sfc cyclogenesis late Sunday/early Monday over the MD MS VLY. NAM appears to catch onto this solution and is the preferred model for now regarding the details of this particular event. Airmass undergoes substantial changes during the day Sunday so will be bumping up cloud cloud cover which previous forecaster has already done. Wind forecast also looks to be in good shape for now as well. However, it may need to be tweaked upward slightly especially if we see this secondary low develop across the Mid MS VLY. Will bump pops to 30% as a few perturbations are hinted at in the mean flow aloft as we start to destabilize our airmass as the flow becomes nearly entirely southerly in the low levels as the shortwave trof approaches. Sunday evening will also go with 20% pops as we will remain a bit too far away from the main forcing to see much in the way of non-seabreeze forced daytime convection. Long Term... Monday things get a bit murky. NAM is the preferred model here as GFS begins to suffer from convective feedback and develops a sfc low over ERN TX which then plays a bit of havoc with the timing regarding the rest of the features. NAM however continues to develop the mid ms vly sfc low, warmfrontogenesis associated with the sfc low occurs across WRN FL/SRN AL Monday afternoon/evening. The airmass undergoes substantial modification as the shortwave appraoches and becomes rather unstable with SBCAPEs indicated around 2000 j/kg with deep layer shear increasing. NAM is a touch further south again tonight with the main upper level energy which increases deep layer shear as the convection gets underway. If this solution were to verify a rather convectively active period can be expected invof the warm front during the afternoon and evening hours Monday, with severe weather well within the realm of possibility, especially if we see a verification of the GFSs suggestion of the LLJ increasing to 50-60kts as the gradient between the trof and a ridge building to the SE verifies. However, for now we still prefer the slightly more conservative NAM which puts it invof 30-35kts. The main questions regard the assumptions made in this forecast regarding the sfc cyclogenesis and the NAMs general handling of the fine scale features needed to produce such an event. Will however bump the Monday/Monday night period to 60 pops. Tuesday is a bit tricky with ECMWF dragging the frontal system behind til about 18z Tuesday with the NAM having us nearly completely cleared out by about 12z. Will for now go with 50% pops assuming we see a slight slowing of the system which is essentially a coin flip regarding the number of available permutations this system may take. More things will slow this system down (deeper UL trof, deeper sfc cyclogenesis, or perhaps weaker than fcst low level windfields) than would speed it up (stronger ridging behind the trof) so will go with that solution on a split difference of ECMWF/NAM. ECMWF is preferred solution for extended due to the substantial impacts of convective feedback from the GFS. MEX MOS temps however appear relatively reasonable for Wed so will go with that general idea as a first guess on post FROPA airmass. Synoptically ECMWF clears us out nicely. as ridging behind the frontal system builds in and our upper level flow becomes rather swift...but zonal.

Hazardous Weather

Hazardous Weather Outlook (Saturday through Wednesday): Organized showers and thunderstorms are likely during the afternoon and overnight hours Monday and early Tuesday as a powerful storm system and cold front moves through the area. There are some questions regarding this system but it appears at this time there is a chance that some of these storms may be severe with isolated tornadoes, damaging winds, and large hail being the main threats. Continue to monitor later forecasts for updates regarding this storm system.

Astronomical and Climatological Data
Moon Phase Last Sunrise 6:37 AM Sunset 6:56 PM	09/16/06 Normal High Record High Normal Low Record Low Temperature 87°F 101°F (1927) 68°F 55°F (1961) September Normal Wettest Driest Precipitation 6.01 in. 24.12 in. (1998) 0.47 in. (1923)

09/16 in Mobile Area Weather History

In 1971 afternoon storms spawned two F2 tornadoes, the first tornado hit south of Stockton in Baldwin County, AL where it demolished at least 2 mobile homes, destroyed a few barns, and damaged at least 10 homes. The second F2 tornado hit east of Fairhope in Baldwin County, AL where it tore apart 2 homes and damaged several other houses. That evening, a storm spawned a tornado near Tibbie in Washington County, AL that destroyed several small buildings. The tornado severely damaged a house and several large chicken houses and downed numerous trees. Also, in 2004 hurricane Ivan spun ashore near Orange Beach in Baldwin County, AL. The storm contained sustained winds over 100 mph at landfall and caused extensive damage from the surge along the coast of Alabama and Florida. Widespread wind damage resulted as it traveled inland towards central Alabama. (Data compiled from NWS Mobile, NWS Birmingham, newspaper articles, USA Archives and HurricaneCity.com)