NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260415_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)
=== ===== === ==== ==== === === === ====
Wed 04/15 12Z 0.13 2807  64  27  13 0.00
Wed 04/15 13Z 0.16 2708  54  25  13 0.00
Wed 04/15 14Z 0.17 2508  53  24  13 0.00
Wed 04/15 15Z 0.23 2411  58  18  13 0.00
Wed 04/15 16Z 0.25 2212  50  68  12 0.00
Wed 04/15 17Z 0.28 2211  47  98  11 0.00
Wed 04/15 18Z 0.31 2212  66  95  10 0.01
Wed 04/15 19Z 0.41 2215  77  84  11 0.00
Wed 04/15 20Z 0.77 2217  84  79  11 0.00
Wed 04/15 21Z 0.69 2315  85  66  11 0.00
Wed 04/15 22Z 0.73 2316  90  53  11 0.00
Wed 04/15 23Z 0.69 2318  92  45  11 0.00
Thu 04/16 00Z 0.82 2521  94  57  11 0.00
Thu 04/16 01Z 0.84 2622  91  57  11 0.00
Thu 04/16 02Z 0.62 2618  88  73  11 0.00
Thu 04/16 03Z 0.58 2618  87  84  11 0.00
Thu 04/16 04Z 0.45 2615  81  83  12 0.00
Thu 04/16 05Z 0.24 2809  76  88  12 0.00
Thu 04/16 06Z 0.26 2508  91  93  10 0.09
Thu 04/16 07Z 0.13 2105  94  97  10 0.06
Thu 04/16 08Z 0.07 1905  93  95  11 0.03
Thu 04/16 09Z 0.07 1906  92  96  12 0.01
Thu 04/16 10Z 0.12 2105  92  92  12 0.04
Thu 04/16 11Z 0.21 2707  94  79  11 0.01
Thu 04/16 12Z 0.24 2810  91  55  11 0.00
Thu 04/16 13Z 0.32 2913  91  33  10 0.00
Thu 04/16 14Z 0.31 2913  89  27  11 0.00
Thu 04/16 15Z 0.25 2911  86  42  11 0.00
Thu 04/16 16Z 0.28 2709  84  68  11 0.00
Thu 04/16 17Z 0.36 2609  83  77  11 0.00
Thu 04/16 18Z 0.41 2309  79  82  12 0.00
Thu 04/16 19Z 0.48 2211  75  77  12 0.00
Thu 04/16 20Z 0.56 2115  75  43  13 0.00
Thu 04/16 21Z 0.71 2117  76  29  13 0.00
Thu 04/16 22Z 0.63 2120  83  22  13 0.00
Thu 04/16 23Z 0.59 2021  86  20  13 0.00
Fri 04/17 00Z 0.51 2018  89  73  13 0.02
Fri 04/17 01Z 0.75 2620  95  91  12 0.56
Fri 04/17 02Z 0.72 2822  88  92  11 0.12
Fri 04/17 03Z 0.72 2720  92  90  10 0.01
Fri 04/17 04Z 0.72 2719  89  85  10 0.01
Fri 04/17 05Z 0.73 2721  91  69  10 0.02
Fri 04/17 06Z 0.65 2721  87  65  10 0.01
Fri 04/17 07Z 0.67 2620  90  72   9 0.01
Fri 04/17 08Z 0.67 2720  97  70   9 0.04
Fri 04/17 09Z 0.59 2820  96  69   9 0.05
Fri 04/17 10Z 0.45 2920  95  75   9 0.03
Fri 04/17 11Z 0.30 3118  96  80   8 0.02
Fri 04/17 12Z 0.18 3318  95  80   8 0.01
Fri 04/17 13Z 0.13 3520  95  79   7 0.00
Fri 04/17 14Z 0.13 0020  95  78   7 0.00
Fri 04/17 15Z 0.19 0020  94  78   6 0.00
Fri 04/17 16Z 0.24 0118  93  78   7 0.00
Fri 04/17 17Z 0.24 0117  92  75   7 0.00
Fri 04/17 18Z 0.27 0115  89  70   7 0.00
Fri 04/17 19Z 0.42 0113  87  61   7 0.00
Fri 04/17 20Z 0.40 0211  86  51   7 0.00
Fri 04/17 21Z 0.43 0210  85  37   7 0.00
Fri 04/17 22Z 0.28 0309  85  23   7 0.00
Fri 04/17 23Z 0.22 0309  83  19   8 0.00

Run total areal avg QPF for the Central_Greens is: 1.16 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