NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20261005_1800
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)
=== ===== === ==== ==== === === === ====
Mon 10/05 18Z 1.05 2721  89  85   2 0.00
Mon 10/05 19Z 2.33 2823  90  71   2 0.02
Mon 10/05 20Z 3.76 2827  90  77   2 0.03
Mon 10/05 21Z 2.91 2932  91  55   0 0.08
Mon 10/05 22Z 2.16 3032  92  33   0 0.03
Mon 10/05 23Z 2.10 3032  93  39   0 0.01
Tue 10/06 00Z 1.85 3033  93  41  -1 0.01
Tue 10/06 01Z 1.75 3034  93  45  -2 0.01
Tue 10/06 02Z 1.67 3034  93  43  -3 0.00
Tue 10/06 03Z 1.56 3034  95  38  -3 0.01
Tue 10/06 04Z 1.43 3033  94  31  -4 0.00
Tue 10/06 05Z 1.33 3032  94  26  -4 0.00
Tue 10/06 06Z 1.22 3032  93  26  -4 0.00
Tue 10/06 07Z 1.14 3032  92  25  -4 0.01
Tue 10/06 08Z 1.00 3031  92  27  -4 0.01
Tue 10/06 09Z 0.88 3031  93  27  -3 0.00
Tue 10/06 10Z 0.73 3030  92  25  -3 0.00
Tue 10/06 11Z 0.65 3030  91  21  -3 0.00
Tue 10/06 12Z 0.62 3030  89  18  -2 0.00
Tue 10/06 13Z 0.57 3029  86  15  -2 0.00
Tue 10/06 14Z 0.54 3028  81  13  -2 0.00
Tue 10/06 15Z 0.55 3026  76  12  -1 0.00
Tue 10/06 16Z 0.57 3025  70  11  -1 0.00
Tue 10/06 17Z 0.64 3024  62  10  -1 0.00
Tue 10/06 18Z 0.75 3023  55   8   0 0.00
Tue 10/06 19Z 1.08 3023  54   6   0 0.00
Tue 10/06 20Z 2.51 2922  51   5   0 0.00
Tue 10/06 21Z 2.00 2922  49   5   0 0.00
Tue 10/06 22Z 1.42 2922  48   6   0 0.00
Tue 10/06 23Z 1.33 2922  48  10   0 0.00
Wed 10/07 00Z 1.04 2921  46  17   0 0.00
Wed 10/07 01Z 0.83 2921  44  31   0 0.00
Wed 10/07 02Z 0.67 2919  42  45   0 0.00
Wed 10/07 03Z 0.57 2917  40  59   0 0.00
Wed 10/07 04Z 0.51 2816  37  68   1 0.00
Wed 10/07 05Z 0.50 2715  35  76   1 0.00
Wed 10/07 06Z 0.47 2615  30  57   2 0.00
Wed 10/07 07Z 0.47 2617  31  55   3 0.00
Wed 10/07 08Z 0.45 2618  33  80   4 0.00
Wed 10/07 09Z 0.47 2619  41  86   4 0.00
Wed 10/07 10Z 0.53 2621  55  89   4 0.00
Wed 10/07 11Z 0.55 2522  61  94   5 0.00
Wed 10/07 12Z 0.53 2422  67  97   5 0.00
Wed 10/07 13Z 0.52 2423  72  96   6 0.00
Wed 10/07 14Z 0.54 2325  74  96   6 0.01
Wed 10/07 15Z 0.52 2326  73  96   6 0.02
Wed 10/07 16Z 0.51 2227  67  97   7 0.01
Wed 10/07 17Z 0.56 2227  57  94   7 0.00
Wed 10/07 18Z 0.57 2226  55  91   6 0.00
Wed 10/07 19Z 0.55 2225  49  85   7 0.01
Wed 10/07 20Z 0.57 2224  53  85   7 0.00
Wed 10/07 21Z 0.64 2225  58  84   7 0.00
Wed 10/07 22Z 0.69 2226  67  90   6 0.00
Wed 10/07 23Z 0.74 2228  71  87   6 0.00
Thu 10/08 00Z 0.75 2229  75  89   6 0.00
Thu 10/08 01Z 0.79 2330  77  87   6 0.00
Thu 10/08 02Z 0.80 2331  82  86   6 0.00
Thu 10/08 03Z 0.80 2330  87  85   7 0.01
Thu 10/08 04Z 0.76 2430  90  81   7 0.01
Thu 10/08 05Z 0.74 2429  92  83   7 0.01

Run total areal avg QPF for the greens is: 0.30 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