NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20261005_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)
=== ===== === ==== ==== === === === ====
Mon 10/05 18Z 1.03 2721  88  85   3 0.00
Mon 10/05 19Z 1.69 2823  91  78   2 0.02
Mon 10/05 20Z 4.58 2826  89  69   2 0.03
Mon 10/05 21Z 2.99 2932  91  70   1 0.10
Mon 10/05 22Z 1.88 3031  91  34   0 0.03
Mon 10/05 23Z 1.84 3031  92  38   0 0.01
Tue 10/06 00Z 1.57 3032  92  36  -1 0.01
Tue 10/06 01Z 1.37 3033  91  40  -2 0.00
Tue 10/06 02Z 1.30 3033  92  39  -2 0.00
Tue 10/06 03Z 1.17 3032  94  33  -3 0.00
Tue 10/06 04Z 1.11 3031  93  24  -3 0.00
Tue 10/06 05Z 1.05 3031  93  20  -3 0.00
Tue 10/06 06Z 0.89 3030  91  17  -3 0.00
Tue 10/06 07Z 0.78 3030  90  16  -3 0.00
Tue 10/06 08Z 0.72 3030  90  17  -3 0.00
Tue 10/06 09Z 0.65 3030  90  18  -3 0.00
Tue 10/06 10Z 0.54 3029  90  16  -2 0.00
Tue 10/06 11Z 0.49 3130  88  14  -2 0.00
Tue 10/06 12Z 0.48 3030  86  13  -2 0.00
Tue 10/06 13Z 0.45 3029  82  10  -2 0.00
Tue 10/06 14Z 0.43 3027  75   8  -1 0.00
Tue 10/06 15Z 0.45 3026  70   7  -1 0.00
Tue 10/06 16Z 0.48 3025  61   6   0 0.00
Tue 10/06 17Z 0.55 3024  53   6   0 0.00
Tue 10/06 18Z 0.64 3023  48   5   0 0.00
Tue 10/06 19Z 1.03 3022  51   3   0 0.00
Tue 10/06 20Z 2.94 2921  50   3   0 0.00
Tue 10/06 21Z 2.26 2921  47   4   0 0.00
Tue 10/06 22Z 1.47 2920  46   7   0 0.00
Tue 10/06 23Z 1.31 2921  45  14   0 0.00
Wed 10/07 00Z 0.93 2920  43  23   0 0.00
Wed 10/07 01Z 0.66 2919  41  40   0 0.00
Wed 10/07 02Z 0.49 2917  38  54   0 0.00
Wed 10/07 03Z 0.42 2916  34  67   1 0.00
Wed 10/07 04Z 0.38 2814  31  72   1 0.00
Wed 10/07 05Z 0.39 2714  28  74   2 0.00
Wed 10/07 06Z 0.42 2615  23  52   2 0.00
Wed 10/07 07Z 0.44 2617  28  53   3 0.00
Wed 10/07 08Z 0.43 2619  37  74   4 0.00
Wed 10/07 09Z 0.44 2620  40  84   5 0.00
Wed 10/07 10Z 0.50 2622  52  87   5 0.00
Wed 10/07 11Z 0.53 2523  58  91   5 0.00
Wed 10/07 12Z 0.54 2523  60  96   6 0.00
Wed 10/07 13Z 0.54 2423  66  94   6 0.00
Wed 10/07 14Z 0.56 2423  66  95   6 0.00
Wed 10/07 15Z 0.54 2323  66  94   6 0.01
Wed 10/07 16Z 0.53 2224  63  96   7 0.00
Wed 10/07 17Z 0.58 2225  56  93   7 0.00
Wed 10/07 18Z 0.61 2224  48  88   7 0.00
Wed 10/07 19Z 0.60 2223  45  80   7 0.00
Wed 10/07 20Z 0.62 2223  48  79   7 0.00
Wed 10/07 21Z 0.75 2224  58  79   7 0.00
Wed 10/07 22Z 0.79 2225  67  91   6 0.00
Wed 10/07 23Z 0.79 2226  72  91   6 0.00
Thu 10/08 00Z 0.79 2228  75  88   6 0.00
Thu 10/08 01Z 0.86 2330  77  85   6 0.00
Thu 10/08 02Z 0.90 2331  82  86   6 0.00
Thu 10/08 03Z 0.89 2431  87  84   7 0.01
Thu 10/08 04Z 0.84 2430  90  82   7 0.01
Thu 10/08 05Z 0.79 2429  92  82   8 0.01

Run total areal avg QPF for the Central_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