NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260818_0000
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)
=== ===== === ==== ==== === === === ====
Tue 08/18 00Z 0.06 3405  93  94  14 0.00
Tue 08/18 01Z 0.05 3506  90  95  14 0.06
Tue 08/18 02Z 0.06 0008  88  93  14 0.01
Tue 08/18 03Z 0.10 0009  87  81  14 0.00
Tue 08/18 04Z 0.11 0108  87  44  14 0.00
Tue 08/18 05Z 0.09 0107  85  20  14 0.00
Tue 08/18 06Z 0.10 0206  84  15  14 0.00
Tue 08/18 07Z 0.10 0305  83  17  14 0.00
Tue 08/18 08Z 0.07 0303  83  24  14 0.00
Tue 08/18 09Z 0.04 0103  83  35  14 0.00
Tue 08/18 10Z 0.03 0002  82  51  14 0.00
Tue 08/18 11Z 0.03 3503  80  52  13 0.00
Tue 08/18 12Z 0.03 3403  79  46  13 0.00
Tue 08/18 13Z 0.04 3202  79  39  13 0.00
Tue 08/18 14Z 0.04 3203  80  27  13 0.00
Tue 08/18 15Z 0.05 3203  82  22  13 0.00
Tue 08/18 16Z 0.03 3403  83  14  13 0.00
Tue 08/18 17Z 0.06 3202  85  12  13 0.00
Tue 08/18 18Z 0.07 3401  86   8  13 0.01
Tue 08/18 19Z 0.11 3202  85   5  13 0.01
Tue 08/18 20Z 0.30 3004  82   5  13 0.00
Tue 08/18 21Z 0.32 3004  80   7  13 0.00
Tue 08/18 22Z 0.18 3105  78  12  13 0.00
Tue 08/18 23Z 0.10 3103  77  11  13 0.00
Wed 08/19 00Z 0.11 2903  77  10  13 0.00
Wed 08/19 01Z 0.18 2804  77  16  13 0.00
Wed 08/19 02Z 0.21 2905  78  18  13 0.00
Wed 08/19 03Z 0.17 2904  80  13  13 0.00
Wed 08/19 04Z 0.17 2803  82   7  12 0.00
Wed 08/19 05Z 0.24 2805  85   6  12 0.00
Wed 08/19 06Z 0.20 2805  88   9  12 0.00
Wed 08/19 07Z 0.16 2904  90  12  12 0.00
Wed 08/19 08Z 0.16 2804  93   8  12 0.00
Wed 08/19 09Z 0.09 2902  93  10  11 0.00
Wed 08/19 10Z 0.14 2503  92  14  11 0.00
Wed 08/19 11Z 0.22 2505  92  15  11 0.00
Wed 08/19 12Z 0.19 2404  91  17  11 0.00
Wed 08/19 13Z 0.28 2505  92  19  11 0.00
Wed 08/19 14Z 0.30 2405  93  21  11 0.00
Wed 08/19 15Z 0.35 2405  91  22  11 0.00
Wed 08/19 16Z 0.51 2406  88  29  11 0.00
Wed 08/19 17Z 0.63 2406  82  44  12 0.00
Wed 08/19 18Z 0.48 2405  74  67  13 0.00
Wed 08/19 19Z 0.61 2407  70  79  13 0.00
Wed 08/19 20Z 0.39 2407  69  77  13 0.00
Wed 08/19 21Z 0.42 2408  69  87  13 0.00
Wed 08/19 22Z 0.47 2509  73  90  13 0.00
Wed 08/19 23Z 0.54 2410  83  89  13 0.00
Thu 08/20 00Z 0.64 2413  87  79  13 0.00
Thu 08/20 01Z 0.71 2415  90  73  13 0.00
Thu 08/20 02Z 0.76 2516  91  72  13 0.00
Thu 08/20 03Z 0.57 2615  88  64  13 0.00
Thu 08/20 04Z 0.54 2615  90  68  13 0.00
Thu 08/20 05Z 0.46 2714  90  70  13 0.00
Thu 08/20 06Z 0.36 2711  91  59  12 0.00
Thu 08/20 07Z 0.31 2810  92  64  12 0.00
Thu 08/20 08Z 0.29 2910  94  56  11 0.00
Thu 08/20 09Z 0.29 2910  95  58  11 0.00
Thu 08/20 10Z 0.22 3008  94  44  11 0.00
Thu 08/20 11Z 0.20 3009  92  32  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.09 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