Scientific Forecaster Discussion
000 FXUS63 KDMX 102132 AFDDMX Area Forecast Discussion National Weather Service Des Moines IA 332 PM CST Tue Dec 10 2019 .DISCUSSION.../Tonight through Tuesday/ Issued at 331 PM CST Tue Dec 10 2019 Impressive short burst of snow today due to thin stratus situated within the dendritic growth zone. This light snow and flurries is moving off to the southeast with drying occurring into central and northwest IA. The next system will quickly sweep into the state tonight. A weak area of low pressure will move southeast ahead of high pressure overnight with a band snow developing mainly just north/northeast of the surface reflection. This band will be mainly thermally driven with vigorous forcing within a relatively deep dendritic layer of around 5 kft. Supersaturation within this layer looks supportive of larger dendrites which would further support the potential for a short period of intense snowfall rates > 1 inch per hour. As of now, these higher snowfall rates look to be aligned from near Fort Dodge to Marshalltown and Montezuma with a band of snowfall of 1 to 2 inches possible. Much of this snow would fall between midnight and 6 am across the area with the more intense rates lasting an hour or less. Again, the greatest threat will be the snow accumulating quickly on roadways. While the wind is not expected to be a factor, the fluffy nature of the snow with snow ratios near 20:1 would be supportive of snow fog created by vehicles lofting the snow and further reducing visibilities. No headlines at this time but will continue to monitor and adjust the forecast as needed. The snow will end quickly from west to east late tonight into early Wednesday morning as high pressure arrives from the north. The system will help drive another round of cold advection into the state. High temperatures over northern Iowa will again be in the single digits above zero while highs over the south will be in the low 30s. The combination of the cold temperatures and increasing wind Wednesday morning will drop wind chills over far northern Iowa into the 10 below to 15 below range. Another chance for light snow will pass across northern Iowa Wednesday night as warm advection lifts through the state. Drier mid level air should limit precipitation chances into central Iowa though some discrepancies on the amount of low level saturation which could impact drizzle chances. Temperatures Thursday will be warmer over the central and south with highs in the mid to upper 40s, assuming the stratus breaks. The mild conditions will persist into Friday before the next short wave passes by Friday night into Saturday. This system will lead to a transition to a thermal trough dipping into the Midwest and colder temperatures. Some light snow is possible over the weekend but no significant impacts are anticipated. Lower confidence into early next week due to uncertainty in the overall evolution of the Hudson Bay low. && .AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/ Issued at 1116 AM CST Tue Dec 10 2019 A few light snow showers will move through Iowa. As of 17z visibility was down to 1SM at FOD. However, this is very localized and visibility reductions are not expected to be widespread nor impacting the other terminals. Clouds will be patchy. There will be periods where CIGs bounce between MVFR and VFR, with bases between 2500 and 3000 feet. Gusty winds will continue through the afternoon will diminish into the evening hours. Overall, aviation impacts will not be overly harsh through period. && .DMX WATCHES/WARNINGS/ADVISORIES... NONE. &&