National Weather Service United States Department of Commerce

Dangerous Cold Friday Night and Saturday

Cold temperatures and gusty winds will occur Friday night and Saturday. Temperatures between -10 and -20 with sustained winds between 5 and 15 mph will cause wind chills between -20 and -40 for most areas Friday night and Saturday morning. Stronger gusts will cause it to feel colder at times. Winds decrease on Saturday and temperatures rise modestly, raising wind chills into the -10 to -20 range. Read More >

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260121_1800
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 01/21 18Z 0.41 2218  76  72 -14 0.00
Wed 01/21 19Z 0.41 2120  68  84 -14 0.00
Wed 01/21 20Z 0.37 2022  77  88 -13 0.00
Wed 01/21 21Z 0.35 1926  79  87 -12 0.00
Wed 01/21 22Z 0.30 1928  88  89 -10 0.01
Wed 01/21 23Z 0.43 2033  91  94 -10 0.03
Thu 01/22 00Z 0.59 2038  85  91 -11 0.01
Thu 01/22 01Z 0.64 2139  81  91 -10 0.00
Thu 01/22 02Z 0.69 2140  89  94  -9 0.00
Thu 01/22 03Z 0.73 2140  92  93  -9 0.01
Thu 01/22 04Z 0.74 2138  88  93  -8 0.00
Thu 01/22 05Z 0.69 2136  87  89  -7 0.00
Thu 01/22 06Z 0.65 2234  90  84  -6 0.01
Thu 01/22 07Z 0.65 2233  95  82  -6 0.01
Thu 01/22 08Z 0.68 2232  96  72  -6 0.01
Thu 01/22 09Z 0.69 2231  96  59  -6 0.01
Thu 01/22 10Z 0.79 2332  96  72  -7 0.01
Thu 01/22 11Z 0.95 2433  95  88  -7 0.01
Thu 01/22 12Z 1.33 2432  93  90  -9 0.02
Thu 01/22 13Z 1.52 2433  93  79 -10 0.01
Thu 01/22 14Z 1.85 2532  94  51 -11 0.01
Thu 01/22 15Z 1.88 2530  93  72 -11 0.00
Thu 01/22 16Z 2.90 2528  92  69 -12 0.00
Thu 01/22 17Z 4.02 2527  90  61 -12 0.00
Thu 01/22 18Z 6.21 2525  84  62 -11 0.00
Thu 01/22 19Z 8.22 2524  83  56 -11 0.00
Thu 01/22 20Z 6.14 2525  85  51 -11 0.00
Thu 01/22 21Z 2.55 2526  86  39 -11 0.00
Thu 01/22 22Z 4.14 2529  86  53 -12 0.01
Thu 01/22 23Z 2.24 2528  83  42 -12 0.01
Fri 01/23 00Z 2.00 2527  87  50 -13 0.00
Fri 01/23 01Z 2.40 2529  82  52 -14 0.01
Fri 01/23 02Z 2.35 2630  80  44 -14 0.01
Fri 01/23 03Z 1.45 2529  82  43 -14 0.00
Fri 01/23 04Z 1.27 2530  82  47 -15 0.01
Fri 01/23 05Z 1.31 2630  79  45 -15 0.01
Fri 01/23 06Z 1.34 2629  81  40 -16 0.01
Fri 01/23 07Z 1.33 2628  86  37 -16 0.00
Fri 01/23 08Z 1.43 2627  85  36 -17 0.00
Fri 01/23 09Z 1.38 2625  86  31 -17 0.00
Fri 01/23 10Z 1.28 2524  89  28 -17 0.00
Fri 01/23 11Z 1.24 2525  92  47 -17 0.00
Fri 01/23 12Z 0.93 2426  83  55 -16 0.00
Fri 01/23 13Z 1.06 2429  86  42 -16 0.00
Fri 01/23 14Z 1.26 2333  91  14 -16 0.00
Fri 01/23 15Z 2.11 2431  89  22 -16 0.00
Fri 01/23 16Z 8.24 2428  91  28 -16 0.00
Fri 01/23 17Z 5.61 2525  89  43 -16 0.01
Fri 01/23 18Z 14.50 2625  79  45 -17 0.01
Fri 01/23 19Z 13.90 2626  74  49 -18 0.01
Fri 01/23 20Z 14.30 2726  72  53 -18 0.01
Fri 01/23 21Z 12.68 2626  72  54 -19 0.00
Fri 01/23 22Z 5.11 2723  77  68 -20 0.01
Fri 01/23 23Z 2.13 2922  82  70 -20 0.01
Sat 01/24 00Z 2.53 2921  77  65 -21 0.01
Sat 01/24 01Z 2.22 3022  72  65 -22 0.01
Sat 01/24 02Z 1.49 3124  62  65 -23 0.01
Sat 01/24 03Z 1.11 3025  60  57 -23 0.00
Sat 01/24 04Z 1.23 3025  73  57 -24 0.00
Sat 01/24 05Z 3.21 3026  82  40 -25 0.00

Run total areal avg QPF for the Central_Greens is: 0.32 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1