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After a review of the 12Z models, not much has changed in our thinking about tomorrow….. watch the Weather Xtreme video for all of the graphics that go with this discussion.
TONIGHT: We will maintain the risk of a few isolated showers this evening; those will end shortly after sunset and most places will remain dry. To the west, a significant outbreak of severe thunderstorms and tornadoes is possible around the Mississippi Delta; seems like the best combination of instability and shear is between Greenville, MS and Memphis. Our friends out there will be keeping a close eye on radar trends in coming hours.
Those storms will enter Northwest Alabama after midnight, and they still could be severe initially over the northwest corner of the state. But, they should weaken toward daybreak as the air becomes more stable.
TOMORROW: Here are some forecast severe weather parameters for Birmingham during the mid-afternoon:
SBCAPE: 914 j/kg
Lifted Index: -4.3
0 to 3 km helicity: 251.8
850 mb wind speed: 40 knots
500 mb wind speed: 64 knots
(these values from the 12Z NAM)
While those numbers are not overly impressive, they certainly support strong to severe thunderstorms. If we have an outflow boundary in play tomorrow afternoon, that would serve as a focusing mechanism for new storms to fire, and could also mean a tornado threat. If we don’t have any well defined surface boundaries around, the main issues will come from damaging straight line wind and hail.
It still appears the primary window for severe weather will come from 12:00 noon until 8:00 p.m., although early morning storms could be severe over Northwest Alabama as we mentioned above.
Models are continuing to trend drier; the 12Z NAM is only showing 0.31″ for Birmingham, while the GFS is printing 0.91″. Looks like we will need to lower our precipitation forecast a bit; looks like a good average amount will be three-quarters of an inch.
SATURDAY: The showers will end Saturday morning, and a dry slot will mean a chance of sunshine Saturday afternoon. While temperatures will be a bit cooler, the really chilly air remains north of Alabama, so we should rise into the 65 to 70 degree range.
SUNDAY: The last cold snap of the season will begin. A sharp north wind will bring in much cooler air; areas north of Birmingham will have a very hard time getting out of the 40s with a cloudy sky and a chance of scattered light rain. Still looks like low level thickness schemes suggest a chance of snow flakes Sunday night over the northern third of Alabama (flurries), perhaps lasting into Monday morning. It sure won’t feel like April.
HOW COLD? The latest GFS MOS is printing 32 for Monday morning, and 30 for Tuesday morning (for Birmingham). We don’t expect much frost early Monday due to clouds and wind, but frost should be widespread early Tuesday with a clear sky and light wind. We expect the actual range of temperatures at daybreak Tuesday to be between 25 and 35 degrees; mid 20s for the coldest valleys, and mid 30s for the ridge tops. Once again, growers will need to monitor the situation closely in coming days.
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