NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260217_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 02/17 12Z 0.20 2210  90  89  -2 0.00
Tue 02/17 13Z 0.22 2310  91  95  -3 0.00
Tue 02/17 14Z 0.24 2311  94  96  -3 0.01
Tue 02/17 15Z 0.24 2311  95  93  -3 0.01
Tue 02/17 16Z 0.24 2310  95  80  -3 0.00
Tue 02/17 17Z 0.26 2410  96  61  -2 0.01
Tue 02/17 18Z 0.31 2512  97  46  -2 0.01
Tue 02/17 19Z 0.34 2513  98  42  -2 0.01
Tue 02/17 20Z 0.37 2613  97  26  -2 0.01
Tue 02/17 21Z 0.43 2614  97  24  -2 0.01
Tue 02/17 22Z 0.49 2616  97  35  -3 0.01
Tue 02/17 23Z 0.56 2718  96  30  -3 0.01
Wed 02/18 00Z 0.53 2717  91  49  -2 0.01
Wed 02/18 01Z 0.57 2819  86  49  -2 0.01
Wed 02/18 02Z 0.66 2822  85  54  -3 0.01
Wed 02/18 04Z 0.71 2824  79  42  -3 0.01
Wed 02/18 05Z 0.71 2925  77  34  -3 0.01
Wed 02/18 06Z 0.61 2925  74  40  -3 0.01
Wed 02/18 08Z 0.50 2924  64  44  -3 0.01
Wed 02/18 09Z 0.43 3023  61  50  -4 0.01
Wed 02/18 11Z 0.34 3021  58  56  -4 0.01
Wed 02/18 12Z 0.30 3119  54  56  -4 0.01
Wed 02/18 13Z 0.26 3118  48  57  -4 0.01
Wed 02/18 14Z 0.22 3116  46  60  -4 0.01
Wed 02/18 15Z 0.19 3114  43  62  -4 0.01
Wed 02/18 16Z 0.15 3212  41  61  -4 0.01
Wed 02/18 17Z 0.12 3210  40  60  -4 0.00
Wed 02/18 18Z 0.08 3309  40  60  -4 0.00
Wed 02/18 19Z 0.06 3407  46  59  -5 0.00
Wed 02/18 20Z 0.04 3506  50  57  -5 0.00
Wed 02/18 21Z 0.05 0105  54  52  -5 0.00
Wed 02/18 22Z 0.08 0307  57  48  -5 0.00
Wed 02/18 23Z 0.11 0309  52  48  -5 0.00
Thu 02/19 00Z 0.15 0311  46  48  -6 0.00
Thu 02/19 01Z 0.16 0313  45  49  -6 0.00
Thu 02/19 02Z 0.16 0213  48  48  -7 0.01
Thu 02/19 03Z 0.12 0212  50  44  -7 0.00
Thu 02/19 04Z 0.09 0111  48  34  -7 0.00
Thu 02/19 05Z 0.06 0111  45  27  -7 0.00
Thu 02/19 06Z 0.04 0110  45  17  -7 0.00
Thu 02/19 07Z 0.03 0010  45   7  -7 0.00
Thu 02/19 08Z 0.03 0011  45   2  -7 0.00
Thu 02/19 09Z 0.02 0011  44   3  -7 0.00
Thu 02/19 10Z 0.03 0012  42   2  -7 0.00
Thu 02/19 11Z 0.03 0012  39   3  -7 0.00
Thu 02/19 12Z 0.04 0010  37   4  -7 0.00
Thu 02/19 13Z 0.05 0108  35   5  -7 0.00
Thu 02/19 14Z 0.04 0105  34   7  -6 0.00
Thu 02/19 15Z 0.03 3503  34  10  -6 0.00
Thu 02/19 17Z 0.07 2902  33  13  -5 0.00
Thu 02/19 18Z 0.07 2702  33  12  -5 0.00
Thu 02/19 19Z 0.08 2602  37  12  -4 0.00
Thu 02/19 20Z 0.10 2503  41  17  -4 0.00
Thu 02/19 21Z 0.13 2504  40  30  -4 0.00
Thu 02/19 22Z 0.16 2506  36  30  -4 0.00
Thu 02/19 23Z 0.19 2507  28  31  -4 0.00

Run total areal avg QPF for the greens is: 0.24 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