Issued: 8pm on Tuesday, December 14th 2021
Technical Forecast Discussion
Short Term (Tuesday 12-14-2021 through Thursday 12-16-2021)
Short term forecast period is starting out with a fairly impressive presentation of upper level ridge over all of Ohio Valley region as +3 standard deviations is showing up as of Tuesday afternoon and have been under this intensifying ridge over past 2 days or so and we have reached the peak intensity of this ridge as our area is under impressive 582dm height. Looking at the surface level, high pressure moved over parts of central Appalachians region which resulted in a southwesterly flow to help bringing in even more milder air from deep south region. Tuesday featured plenty of sunshine in our region with no weather delays. Now as we move through Tuesday night, while this ridge still expected to remain strong for our area, its overall intensity is expected to take a slight downturn as the ridge will now also be moving eastward at the same time and be centered over far southern portions of Ontario by Wednesday morning. With continued southwesterly flow from high pressure, look for temperatures warm up even further from prior day, but there will be more clouds likely in play for our region as warm front is expected to lift northward through our area. Our area could see isolated rain showers at times on Wednesday otherwise dry conditions for most of us. The reason why our ridge will weaken and move eastward along with increase clouds associated with lifting northward has to do with formation of surface low pressure over eastern Colorado region. There is another active trough which entered west coast earlier Tuesday which is then expected to emerge out over eastern Rockies of Colorado by Wednesday afternoon and quickly head into the High Plains region by Wednesday evening which will be the reason for surface low formation as it is also attacking the ridge to its east and starting to weakening it. This Colorado low will race northeastward into far southwestern Minnesota by Wednesday evening and lift continue to northward into southcentral Ontario by Thursday morning. As this low is racing, there might be a severe weather event with damaging winds and tornado for much of central Iowa and far southern Minnesota while snow breaks out over Dakotas. Another impressive thing to note will be very high winds (50-70mph gusts) in middle of the country due strong pressure gradient between the low and high pressure in eastern U.S.. Fortunately for our area, we will not be in this tight gradient for gusty winds on Wednesday nor we will deal with severe weather and snow like High Plains and northern Midwest region. Now as we move into Thursday morning period, cold front associated with this system will be on the move and be located somewhere in central Michigan, northwestern Indiana, and southern Illinois area by Thursday morning with showers and storms developing out ahead of cold front over the same region. One good thing is moisture return from Gulf of Mexico does not appear to be nearly as rich at all as it was for this past Friday’s severe weather event and this is why any severe weather threat anywhere in Ohio Valley looks to be very low at this time. Best chances of rainfall will move into our area will be on Thursday afternoon and evening with front clearing our region by this time and it looks like rainfall totals will be 0.10″-0.25″ range by Friday morning. Another thing to keep in mind is given that high pressure continues to move offshore of eastern U.S. with surface low lifting into Ontario by Thursday, the gradient zone will weaken so high wind threat will decrease for most areas. Despite this, our region will be able to get into 10-15mph sustained wind with gusts near 30mph for brief period on afternoon hours of Thursday before cold front passes. Looking back at the upper levels, the ridge does get pushed eastward and flattened down a little during Thursday morning into evening hours for our region as the short-wave directly moves into strong ridge axis and beats it down. Looking at temperatures, our highs on Tuesday looks to be near in upper 50’s which further warms up into lower 60’s on Wednesday and Thursday. Morning low temperatures remaining in lower 30’s Tuesday night before its a warm one in upper 40’s Wednesday night before it cools down into upper 30’s for Thursday nighttime. Temperature anomalies will be remain strongly above normal at 14°F-18°F range for our area with near record highs possible by Thursday.
Long Term (Friday 12-17-2021 through Monday 12-20-2021)
Long term period begins with the beaten down ridge to slightly start to flex northward again by early Friday morning as main axis lies over Mid-Atlantic region and continue to hold its grip for all the way from central and southern Plains, Ohio Valley, and most of Northeast region with weak surface high pressure right over southern Michigan area. Temperatures on Friday actually don’t cool down that much significantly for our region as wind flow look to turn again from south direction later on the same day. Our weather pattern starts to take more of an interesting turn as we start the long term period given that shortwave trough which looks to come down into northern Midwest and High Plains region. At the same time, we have a upper level high centered over southwestern Atlantic with its far western ridge periphery located from southeastern Texas to central Arkansas and western Tennessee which then curves eastward over Kentucky and Virginia’s region from Friday afternoon to Saturday afternoon period. This is the region where we have multiple waves of wind energy moving with the help from southern branch of jet stream. As the moisture streams northward and interacts with a stalled boundary in this region, steady bouts of rainfall breaks out as of result with low pressure zone riding along this boundary. Thankfully for us colder air will be quite a ways to our north, otherwise these types of setups are notorious for heavy wintry mix precipitation this time of the year. Despite no cold air, temperatures on Friday appear to be fairly raw with cold rain expected, but it does look like warm front lifts north on Friday night into Saturday so things will feel little better. Interestingly, there is some expectation of snow and ice once you get into Michigan through northeastern parts of U.S. and will not likely trend southward into our area. There is still some uncertainty as to where the heaviest band of rainfall will be set up for and early indications suggest that it could produce over 2″ of rainfall somewhere otherwise a general 1″+ of rainfall appears to be likely for our region. One important thing to note is that we have had quite a few rain events recently leading to more of a saturated soils and given the combination of easier runoffs this time of the year is easier due to vegetation absorbing less water and decent rainfall in shorter time period, there is a non-zero risk of flooding potential with this system as well. Once we head into Saturday evening through Sunday afternoon, this shortwave trough moves through our area quickly and this will deliver colder air mass into our area from Saturday evening through Monday morning time frame. Given that I am expecting temperatures to fall several degrees below freezing by Saturday night along with heavier rainfall totals earlier in the day, I believe there is an elevated threat of any standing water or wet surfaces in general to potentially freeze over. While I don’t this this threat of any flash freeze is very high due to a period where things do have chance to completely runoff and dry out in some wind before colder air comes in, but this is something to keep an eye on as we get closer to this event. Looking back at the upper level height, the upper level ridge remains over Mid-Atlantic region on Saturday which becomes more zonal to slight troughing Saturday night into Sunday afternoon before another area of ridge starts to develop over northcentral portions of U.S. There is a surface high pressure associated with this ridge over western Ohio Valley as of Sunday afternoon. This high pressure would be close enough to our area for clear and bright conditions under chilly northerly flow for one day. By Monday, this high pressure area moves eastward and we have a return of southerly flow behind it and allow warming trend to start once again along with few more clouds able to works its way into our area. At upper levels, the ridge to our west moves into our area and weakens again so there is actually more of zonal flow despite higher than normal height levels. Looking at temperatures, our highs on Friday looks to be near in mid 40’s which further warms up into lower 50’s on Saturday before we cool down to upper 30’s by Sunday which then warms up slightly into middle 40’s by Monday. Early evening temperatures remaining in lower 40’s before they start to rise Friday night but we cool down into middle 20’s by Saturday night. This was the reason why I am concerned about freeze over of wet surfaces. Low temperatures continue to hold into middle 20’s for Sunday and Monday night as well with high pressure under control. Temperature anomalies will come down quite significantly from short term period, but things will still end up in 3°F-5°F range above normal for this time of the year.
