775 FOUS11 KWBC 040704 QPFHSD Probabilistic Heavy Snow and Icing Discussion NWS Weather Prediction Center College Park MD 204 AM EST Mon Nov 4 2024 Valid 12Z Mon Nov 04 2024 - 12Z Thu Nov 07 2024 ...CO/NM border... Day 1... Upper low over NM this morning will lift northeastward across the TX Panhandle this evening. Snow on the NW side of the low within a region of modest PVA and enhanced upslope into the Raton Mesa will continue for the first part of D1 before tapering off later this evening and overnight. Lighter snow will extend eastward into the far western OK Panhandle as rain changes to snow. WPC probabilities for at least 8 inches of snow are >50% above 9000-10,000ft over portions of central/northern NM and across the CO line. ...Northwest and Northern/Central Rockies... Days 1-2... Next system coming into the PacNW will be the last for at least a little bit in what has been quite a busy stretch. Warm front will move ashore today bringing in a surge of moisture and rising snow levels up to around 4000ft to the north and 6000ft to the south over the WA Cascades, but only rising to around 5000ft farther east toward the Divide. Strong and favorable upslope flow will maximize over the WA Cascades where a few feet of snow will be possible at the higher peaks. By late in the evening and overnight into Tuesday, snow levels will fall to around 3000ft bringing accumulating snow to many of the lower passes across the Cascades. WPC probabilities for at least 8 inches of snow are >50% above 3500ft or so. Upper jet will continue inland and promote moderate snow across the northern ID ranges into northwestern Montana. Into D2, the mid-level vort will deepen and split, with the northern portion closing off along the MT/Canadian border before pivoting back southward Tuesday evening over central MT. This will maintain modest snow over the central MT terrain (i.e., Little Belt and Big Snowy Mountains) on upslope northerly flow. There, WPC probabilities for at least 8 inches of snow D2 are >50% above 4000ft or so. The southern portion of the mid-level trough will dig into the Great Basin through early Wednesday, spreading snow across UT/CO where several inches are likely, especially into the CO Rockies. By the end of D2, an upper low will start to close off over the Four Corners region, setting up the next phase of the system. ...Four Corners... Day 3... Aforementioned upper low is forecast to be situated over eastern UT early Wednesday morning and will likely sink southward through the day to a position over eastern AZ by the end of D3. This will keep a relatively consistent SW to S flow over northern NM into southern CO, which is quite favorable for upslope enhancement over the San Juans and into the Sangre de Cristos among other ranges. Multiple waves of PVA will rotate around the upper low and across the region, favoring moderate to heavy snow at times with a high likelihood (>60% chance) of moderate impacts per the probabilistic WSSI. WPC probabilities for at least 8 inches of snow are >50% above 6000-8000ft and probabilities for at least 4 inches >50% down to around 5000-7000ft. Colder air filtering into northeastern CO will also promote light to perhaps modest snow over the I-25 corridor with heavier totals likely into the Palmer Divide. Heavy snow is forecast to continue past the end of D3 as the system slowly moves through the region. Please see the Winter Weather Outlook and the Probabilistic Winter Storm Severity Index (WSSI-P) for more information. The probability of significant ice across the CONUS is less than 10 percent. Fracasso $$