NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260704_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)
=== ===== === ==== ==== === === === ====
Sat 07/04 00Z 0.66 2919  71  87  19 0.00
Sat 07/04 01Z 0.67 2920  74  93  18 0.00
Sat 07/04 02Z 0.69 3020  78  91  18 0.00
Sat 07/04 03Z 0.71 2921  78  86  17 0.00
Sat 07/04 04Z 0.69 3021  77  89  16 0.00
Sat 07/04 05Z 0.67 3021  83  88  16 0.00
Sat 07/04 06Z 0.56 3021  86  82  16 0.00
Sat 07/04 07Z 0.48 3019  89  81  17 0.00
Sat 07/04 08Z 0.45 3018  88  78  16 0.00
Sat 07/04 09Z 0.44 3018  89  77  16 0.00
Sat 07/04 10Z 0.42 3017  90  67  15 0.00
Sat 07/04 11Z 0.40 3017  91  62  15 0.00
Sat 07/04 12Z 0.41 3016  92  64  15 0.00
Sat 07/04 13Z 0.43 3016  91  64  15 0.00
Sat 07/04 14Z 0.47 3015  90  61  15 0.00
Sat 07/04 15Z 0.50 3014  87  62  15 0.00
Sat 07/04 16Z 0.71 3112  86  73  15 0.01
Sat 07/04 17Z 0.89 3115  88  71  15 0.11
Sat 07/04 18Z 1.02 3114  89  71  15 0.03
Sat 07/04 19Z 1.51 3213  86  72  14 0.01
Sat 07/04 20Z 1.31 3215  81  68  14 0.03
Sat 07/04 21Z 1.18 3214  77  60  14 0.00
Sat 07/04 22Z 0.54 3214  74  61  14 0.00
Sat 07/04 23Z 0.31 3313  71  61  14 0.00
Sun 07/05 00Z 0.15 3312  68  59  14 0.00
Sun 07/05 01Z 0.11 3412  67  54  14 0.00
Sun 07/05 02Z 0.10 3411  67  47  13 0.00
Sun 07/05 03Z 0.09 3411  67  46  13 0.00
Sun 07/05 04Z 0.05 3409  67  41  13 0.00
Sun 07/05 05Z 0.06 3410  65  42  13 0.00
Sun 07/05 06Z 0.03 3408  64  40  13 0.00
Sun 07/05 07Z 0.02 3407  63  40  13 0.00
Sun 07/05 08Z 0.03 3405  63  35  12 0.00
Sun 07/05 09Z 0.05 3504  64  23  12 0.00
Sun 07/05 10Z 0.04 3502  63  29  12 0.00
Sun 07/05 11Z 0.04 0002  62  35  12 0.00
Sun 07/05 12Z 0.06 0501  65  34  12 0.00
Sun 07/05 13Z 0.07 1301  69  29  12 0.00
Sun 07/05 14Z 0.15 1501  73  25  12 0.00
Sun 07/05 15Z 0.18 1900  76  19  12 0.00
Sun 07/05 16Z 0.19 2900  78  10  12 0.00
Sun 07/05 17Z 0.21 3101  78  12  12 0.01
Sun 07/05 18Z 0.25 3102  77   8  12 0.00
Sun 07/05 19Z 0.20 3303  76   4  13 0.00
Sun 07/05 20Z 0.12 3403  75   2  13 0.00
Sun 07/05 21Z 0.27 0003  75   2  13 0.00
Sun 07/05 22Z 0.21 0004  75   3  13 0.00
Sun 07/05 23Z 0.29 0205  76   3  13 0.00
Mon 07/06 00Z 0.31 0405  77   3  13 0.00
Mon 07/06 01Z 0.38 0506  76   3  13 0.00
Mon 07/06 02Z 0.56 0609  76   4  12 0.00
Mon 07/06 03Z 0.68 0711  77   4  12 0.00
Mon 07/06 04Z 0.67 0811  75   3  12 0.00
Mon 07/06 05Z 0.59 1011  77   3  12 0.00
Mon 07/06 06Z 0.42 1211  81   3  12 0.00
Mon 07/06 07Z 0.31 1311  83   3  12 0.00
Mon 07/06 08Z 0.28 1313  86   4  12 0.00
Mon 07/06 09Z 0.21 1414  89   5  12 0.00
Mon 07/06 10Z 0.18 1515  86   5  12 0.00
Mon 07/06 11Z 0.21 1416  85   6  11 0.00

Run total areal avg QPF for the Central_Greens is: 0.20 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