Current Conditions at Sanborn Field

Tuesday: Becoming partly cloudy by late morning. High: 70
 

Tuesday Night: Cloudy. Rain likely with thunderstorms possible. Low: 45
 

Wednesday: Partly cloudy. High: 59 

 

Wednesday Night: Mostly cloudy. Low: 41
 

Thursday: Cloudy. Rain possible. High: 48

 

 

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Discussion:

A day of warm temperatures on Tuesday will give way to another taste of winter-like conditions. As the sky partially clears late Tuesday morning, temperatures will reach the upper 60s. This won't last long as a cold front will pass through the area Tuesday evening. Ahead of that cold front, an isolated thunderstorm is not out of the question. Most of the region, however, should see just rain. Behind the front. Temperatures will drop considerably as highs for Wednesday and Thursday struggle to reach 50.

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Forecasters: Travis

Date Issued: 04/05/2022 10:00AM CDT

Technical Discussion: 

 

A cold frontal passage and subsequent deep, long-wave trough will bring precipitation Tuesday night into Wednesday and potential for a late freeze later in the week. There was good agreement between the 06z GFS and NAM regarding temperature, and overall pattern. As such, a blend of the two was used with a heavier lean on the NAM for precipitation Tuesday night into early Wednesday.

NAM and GFS 250-hPa wind and divergence both resolve coupling of jet streaks over the Southeast CONUS and southern Tennessee River Valley. This will keep the bulk of the upper-level dynamics associated with this shortwave well to the south and east of the region. Much weaker divergence will develop ahead of a jet streak off to the NW associated with a rapidly deepening, longwave trough. As this trough deepens, the polar jet streak will surge southward and allow for the eventual infiltration of cold air at the lower levels. 

Model plots of 500-hPa absolute vorticity favor a similar story with circulation (albeit fairly weak in nature) advecting into the region associated with the jet aloft. Thus, dynamics are in place for weaker to moderate forcing for ascent ahead of the amplifying trough. By Thursday, nearing the end of this forecasting period, the deep, upper-level low will sit over the western Great Lakes region aiding and abetting a southern surge of arctic air aloft. 

At this point in the top-down prognostics, model consensus breaks down and a heavier lean is placed on the NAM. Temporally, the period of concern regarding model disagreement comes Tuesday night into Wednesday with the expectation of precipitation. The GFS and NAM differ considerably regarding the amount of moisture present in the mid-levels, and timing. More stock was placed in the NAM due to the lower-level mean wind's origin out of the drier air mass to the SW. A shortwave alluded to earlier will bring active weather to the Southeast, gradually pushing the mT airmass further to the east. The result is a push of the drier cT airmass of the SW CONUS closer to the Midwest and thus should result in a dimihsed supply of moisture. The NAM resolves this well with significantly drier air at 700 hPa. Conversely, the GFS favors a much greater extent of saturated air that pushes through quicker early Wednesday morning. 

 

A deficiency in moisture supported in the 850-hPa wind field as straight westerly winds over TX, and into LA will prevent any significant northward push of Gulf moisture. As the upper-level low deepens, so too does the 850-hPa low. Low-level winds will shift out of the NW and strengthen (nearing 50 knots in northern MO) bringing in much colder air from the north. MSLP and 1000-500-hPa thickness plots back this up with tight, CAA solenoids behind a cold frontal passage favored close to 00z Wednesday. Despite the strong winds mentioned above, winds at the surface are favored to stay below 20 knots. That being said, gusts could result in some breezy conditions on Wednesday. 

GOES visible imagery shows that clearing will ensue late Tuesday morning. This will help temperatures warm up and humidity to increase as Monday night's rain evaporates. Model soundings from both the GFS and NAM show moderate instability (~500 J/kg of CAPE) Tuesday afternoon ahead of the cold front. As such the possibility for convection can't be ruled out. Moving ahead, the upper-level low and its associated cold air aloft will help the air beneath the low stay saturated at 700 hPa going into the end of this forecast period. A look a soundings from both the GFS and NAM suggest this will be limited to the mid-levels resulting in only persistent cloudiness.