Scientific Forecaster Discussion

000 fxus63 kgrb 241720 afdgrb Area forecast discussion National Weather Service Green Bay WI 1220 PM CDT Wed Apr 24 2019 Updated aviation portion for 18z taf issuance Short Thursday issued at 330 am CDT Wed Apr 24 2019 High pressure over the Great Lakes will provide another dry day across the region as it slowly retreats off to the east. Highs today will mainly be in the 60s away from the Great Lakes, with highs in the 50s close to the lake. With the high off to the east, this will allow a weak low pressure system to track through the region later tonight and into Thursday. Recent model runs have slowed down the arrival of this system, with little to no rain expected before midnight save for possibly north-central Wisconsin. The system itself will not tap into Gulf moisture and the dynamics associated with the system are not all that impressive. Therefore quantitative precipitation forecast amounts later tonight into Thursday are expected to stay below one quarter of an inch, with many locations below one tenth of an inch. Lows tonight will only fall into the lower to middle 40s, with highs on Thursday rising into the 60s. Long term...Thursday night through Tuesday issued at 330 am CDT Wed Apr 24 2019 Forecast concerns continue revolve around precip chances as flatten troughing develops in the upper levels over the northern tier of the conus this weekend into next week. Models continue to advertise that two systems could potentially impact the region, one on Saturday and another Monday into Tuesday. The model spread remains rather large with both systems, particularly with the strength of the system on Saturday. Based on model comparisons, will take a general model blend given that the stronger GFS has some support from its ensemble mean. Thursday night through Friday night...a digging shortwave trough will push a secondary cold front across the region on Thursday night. Low and mid-levels remain dry though, so don't see much of a threat of precip. Low clouds behind the front have potential to push into far northern WI late Thursday night into Friday morning, while the flow looks too westerly for those clouds to drop farther south. Temps will continue to cool on Friday with highs mainly in the 50s. Clouds will be on the increase on Friday night ahead of a low pressure system moving across the northern plains. The timing has slowed down slightly, so now Friday night should remain dry. Rest of the forecast...the low pressure system is then projected to track across northern Illinois or far southern Wisconsin on Saturday before departing on Saturday night. Models depict a large swath of qpf north of the low track in the right rear quad of a jet streak and nose of a low level jet. Thermal profiles will be quite interesting as the system draws in 850-925mb temps below 0c from the north. Because precip is expected to occur during the day, warming temps will mitigate the risk of accumulating snow somewhat, but some wet snowflakes and minor accumulations on grassy surfaces appear possible over parts of the area. After a period of dry weather, the models were previously advertising a broad warm advection pattern setting up for Monday into Tuesday. The GFS and Canadian still show this occurring, but the ECMWF and GFS ensemble mean have shifted this pattern south. Uncertainty therefore remains rather large for early next week. && Aviation...for 18z taf issuance issued at 1219 PM CDT Wed Apr 24 2019 Anticipate mainly just mid and high clouds across northeast WI this afternoon into the evening as a cold front gradually approaches from the northwest. This front is forecast to move through the rhi taf site around 09z tonight, the auw/County Warning Area taf sites around 12z Thursday, the grb/atw taf sites around 15z Thursday and move through the mtw taf site toward midday. Initially, there is a general lack of lift, forcing and moisture associated with this front, however this changes Thursday afternoon over the southeast half of the state as better moisture and stronger mid-level forcing arrives. This will bring a better chance of seeing rain showers to central and east-central WI, along with a band of MVFR cigs/vsbys as the rain moves through this part of the state. && Hydrology... issued at 330 am CDT Wed Apr 24 2019 Rivers and streams across northeast WI remain at high levels. This includes high flows in and around area dams as excess water is being released from earlier rainfall and snowmelt. The lack of significant rainfall through the end of the week should help mitigate flooding from additional rainfall. Please monitor the latest river forecasts for further information on flooding in your local area. && Grb watches/warnings/advisories... none. && $$

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