Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261025_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)
=== ===== === ==== ==== === === === ====
Sun 10/25 18Z 0.15 2705  31   8   8 0.00
Sun 10/25 19Z 0.16 2706  31   9   9 0.00
Sun 10/25 20Z 0.17 2606  28  11   9 0.00
Sun 10/25 21Z 0.17 2507  24  13  10 0.00
Sun 10/25 22Z 0.20 2508  20  14  10 0.00
Sun 10/25 23Z 0.23 2510  19  13  10 0.00
Mon 10/26 00Z 0.27 2512  17  12  10 0.00
Mon 10/26 01Z 0.30 2613  19  14  11 0.00
Mon 10/26 02Z 0.33 2615  18  18  10 0.00
Mon 10/26 03Z 0.36 2717  15  17  10 0.00
Mon 10/26 04Z 0.34 2717  16  15  11 0.00
Mon 10/26 05Z 0.31 2716  15  15  11 0.00
Mon 10/26 06Z 0.28 2714  13  15  11 0.00
Mon 10/26 07Z 0.29 2714  13  14  11 0.00
Mon 10/26 08Z 0.30 2815  13  14  11 0.00
Mon 10/26 09Z 0.30 2814  13  15  11 0.00
Mon 10/26 10Z 0.31 2915  14  15  10 0.00
Mon 10/26 11Z 0.32 2915  17  17  10 0.00
Mon 10/26 12Z 0.35 2816  23  28  10 0.00
Mon 10/26 13Z 0.40 2819  34  56   9 0.00
Mon 10/26 14Z 0.45 2921  45  67   9 0.00
Mon 10/26 15Z 0.47 2922  59  76   9 0.00
Mon 10/26 16Z 0.48 2922  73  81   8 0.00
Mon 10/26 17Z 0.47 2921  87  88   8 0.00
Mon 10/26 18Z 0.45 2921  94  89   7 0.01
Mon 10/26 19Z 0.42 2920  95  89   6 0.01
Mon 10/26 20Z 0.41 3019  94  90   5 0.02
Mon 10/26 21Z 0.39 3019  95  92   4 0.02
Mon 10/26 22Z 0.40 3021  93  88   4 0.02
Mon 10/26 23Z 0.43 3124  93  86   3 0.01
Tue 10/27 00Z 0.39 3225  89  77   2 0.01
Tue 10/27 01Z 0.34 3227  88  78   0 0.00
Tue 10/27 02Z 0.23 3324  86  62   0 0.01
Tue 10/27 03Z 0.15 3322  83  47  -1 0.00
Tue 10/27 04Z 0.12 3321  83  27  -2 0.00
Tue 10/27 05Z 0.11 3322  80  13  -2 0.00
Tue 10/27 06Z 0.07 3422  76   8  -2 0.00
Tue 10/27 07Z 0.05 3422  72   4  -2 0.00
Tue 10/27 08Z 0.05 3422  65   1  -1 0.00
Tue 10/27 09Z 0.05 3422  60   1  -1 0.00
Tue 10/27 10Z 0.03 3422  54   3  -1 0.00
Tue 10/27 11Z 0.02 3423  47   5   0 0.00
Tue 10/27 12Z 0.02 3422  42   6   0 0.00
Tue 10/27 13Z 0.02 3520  42   7   0 0.00
Tue 10/27 14Z 0.01 3418  44   7   0 0.00
Tue 10/27 15Z 0.02 3416  44   7   0 0.00
Tue 10/27 16Z 0.03 3414  43   8   0 0.00
Tue 10/27 17Z 0.04 3412  42   9   0 0.00
Tue 10/27 18Z 0.04 3412  41   9   0 0.00
Tue 10/27 19Z 0.05 3312  39   8   0 0.00
Tue 10/27 20Z 0.06 3312  35   8   0 0.00
Tue 10/27 21Z 0.04 3412  29   8   0 0.00
Tue 10/27 22Z 0.05 3313  24   9   0 0.00
Tue 10/27 23Z 0.04 3413  19  10   0 0.00
Wed 10/28 00Z 0.02 3413  17  11   0 0.00
Wed 10/28 01Z 0.02 3411  17  14   1 0.00
Wed 10/28 02Z 0.02 3410  17  17   1 0.00
Wed 10/28 03Z 0.01 3409  16  20   1 0.00
Wed 10/28 04Z 0.01 3407  15  21   1 0.00
Wed 10/28 05Z 0.01 3406  15  20   2 0.00

Run total areal avg QPF for the Central_Greens is: 0.11 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