NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260809_1200
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 08/09 12Z 0.52 2817  88  83  15 0.00
Sun 08/09 13Z 0.48 2816  85  44  15 0.00
Sun 08/09 14Z 0.51 2816  83  13  15 0.00
Sun 08/09 15Z 0.64 2816  84   9  14 0.00
Sun 08/09 16Z 0.86 2716  84  23  14 0.00
Sun 08/09 17Z 1.03 2715  86  28  14 0.02
Sun 08/09 18Z 1.03 2715  87  25  14 0.01
Sun 08/09 19Z 1.35 2814  80  23  14 0.01
Sun 08/09 20Z 2.44 2815  77  25  14 0.00
Sun 08/09 21Z 2.65 2816  75  28  14 0.00
Sun 08/09 22Z 1.12 2816  73  26  14 0.00
Sun 08/09 23Z 1.02 2816  79  25  14 0.00
Mon 08/10 00Z 0.75 2916  79  27  14 0.00
Mon 08/10 01Z 0.51 2915  68  28  15 0.00
Mon 08/10 02Z 0.37 2915  60  32  16 0.00
Mon 08/10 03Z 0.32 3015  58  35  16 0.00
Mon 08/10 04Z 0.27 3014  58  37  16 0.00
Mon 08/10 05Z 0.22 3114  57  39  16 0.00
Mon 08/10 06Z 0.16 3213  55  38  16 0.00
Mon 08/10 07Z 0.10 3310  53  35  15 0.00
Mon 08/10 08Z 0.09 3208  53  36  15 0.00
Mon 08/10 09Z 0.07 3307  55  34  15 0.00
Mon 08/10 10Z 0.03 3404  57  35  14 0.00
Mon 08/10 11Z 0.03 3401  60  41  14 0.00
Mon 08/10 12Z 0.05 1504  61  36  14 0.00
Mon 08/10 13Z 0.02 1707  62  30  14 0.00
Mon 08/10 14Z 0.10 1809  63  30  14 0.00
Mon 08/10 15Z 0.29 1910  62  37  14 0.00
Mon 08/10 16Z 0.74 2010  63  38  14 0.00
Mon 08/10 17Z 1.15 2112  61  35  14 0.00
Mon 08/10 18Z 0.67 2113  68  34  14 0.00
Mon 08/10 19Z 0.54 2115  84  53  14 0.00
Mon 08/10 20Z 0.40 2115  84  83  14 0.00
Mon 08/10 21Z 0.20 1916  81  97  14 0.01
Mon 08/10 22Z 0.26 1919  90  94  14 0.05
Mon 08/10 23Z 0.48 2118  95  94  14 0.07
Tue 08/11 00Z 0.61 2220  96  93  15 0.02
Tue 08/11 01Z 0.66 2321  96  80  15 0.06
Tue 08/11 02Z 0.76 2422  97  61  15 0.08
Tue 08/11 03Z 0.76 2521  94  62  15 0.05
Tue 08/11 04Z 0.65 2619  96  51  15 0.05
Tue 08/11 05Z 0.69 2721  97  58  14 0.06
Tue 08/11 06Z 0.69 2720  96  64  14 0.07
Tue 08/11 07Z 0.77 2822  96  46  14 0.04
Tue 08/11 08Z 0.75 2822  93  30  13 0.01
Tue 08/11 09Z 0.82 2825  95  32  13 0.02
Tue 08/11 10Z 0.83 2927  97  36  12 0.03
Tue 08/11 11Z 0.75 2928  93  22  12 0.02
Tue 08/11 12Z 0.70 3027  92  18  12 0.01
Tue 08/11 13Z 0.66 3026  88  16  12 0.01
Tue 08/11 14Z 0.60 3025  86  13  12 0.01
Tue 08/11 15Z 0.53 3023  81  14  12 0.01
Tue 08/11 16Z 0.57 3022  77  12  12 0.00
Tue 08/11 17Z 0.68 3021  73  15  12 0.00
Tue 08/11 18Z 0.82 3120  69  17  12 0.00
Tue 08/11 19Z 0.92 3119  65  17  12 0.00
Tue 08/11 20Z 0.78 3216  64  17  12 0.00
Tue 08/11 21Z 0.82 3115  67  18  12 0.00
Tue 08/11 22Z 0.74 3114  72  19  12 0.00
Tue 08/11 23Z 0.62 3013  81  21  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.72 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