NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260413_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)
=== ===== === ==== ==== === === === ====
Mon 04/13 12Z 0.61 2434  70  79  11 0.00
Mon 04/13 13Z 0.60 2432  71  77  11 0.00
Mon 04/13 14Z 0.60 2431  71  82  11 0.00
Mon 04/13 15Z 0.69 2334  68  58  11 0.00
Mon 04/13 16Z 0.79 2334  67  62  11 0.00
Mon 04/13 17Z 1.10 2436  76  90  10 0.00
Mon 04/13 18Z 1.96 2436  79  82   9 0.00
Mon 04/13 19Z 5.37 2435  83  91   9 0.00
Mon 04/13 20Z 2.29 2435  90  98   9 0.02
Mon 04/13 21Z 1.39 2639  96  95   9 0.07
Mon 04/13 22Z 1.42 2738  96  93   9 0.04
Mon 04/13 23Z 1.34 2736  96  88   9 0.02
Tue 04/14 00Z 1.24 2736  97  89   9 0.04
Tue 04/14 01Z 1.13 2834  97  78   8 0.02
Tue 04/14 02Z 1.03 2833  97  61   8 0.01
Tue 04/14 03Z 0.91 2931  97  55   8 0.01
Tue 04/14 04Z 0.75 2928  95  50   7 0.01
Tue 04/14 05Z 0.62 3025  94  46   7 0.01
Tue 04/14 06Z 0.52 2922  93  33   8 0.01
Tue 04/14 07Z 0.46 2921  91  28   8 0.01
Tue 04/14 08Z 0.41 2919  89  28   8 0.01
Tue 04/14 09Z 0.41 2819  88  27   8 0.01
Tue 04/14 10Z 0.37 2817  88  25   8 0.01
Tue 04/14 11Z 0.35 2817  86  21   9 0.01
Tue 04/14 12Z 0.27 2814  82  21  10 0.00
Tue 04/14 13Z 0.23 2711  78  20  10 0.00
Tue 04/14 14Z 0.21 2410  76  20  11 0.00
Tue 04/14 15Z 0.24 2213  74  20  12 0.00
Tue 04/14 16Z 0.32 2117  78  23  11 0.00
Tue 04/14 17Z 0.40 2120  83  44  11 0.00
Tue 04/14 18Z 0.50 2121  90  43  11 0.00
Tue 04/14 19Z 0.66 2021  83  64  12 0.00
Tue 04/14 20Z 1.48 1924  79  47  13 0.00
Tue 04/14 21Z 0.99 2123  90  90  12 0.11
Tue 04/14 22Z 1.04 2429  93  83  12 0.26
Tue 04/14 23Z 1.19 2630  97  71  11 0.01
Wed 04/15 00Z 1.31 2630  98  58  11 0.02
Wed 04/15 01Z 1.20 2729  98  40  10 0.02
Wed 04/15 02Z 1.05 2728  98  35  10 0.03
Wed 04/15 03Z 0.84 2726  98  29  10 0.03
Wed 04/15 04Z 0.74 2825  98  20   9 0.03
Wed 04/15 05Z 0.63 2924  98  16   9 0.03
Wed 04/15 06Z 0.45 2922  97  13   8 0.02
Wed 04/15 07Z 0.33 2918  93  10   9 0.01
Wed 04/15 08Z 0.28 2916  87  10  10 0.01
Wed 04/15 09Z 0.26 2814  81  10  11 0.01
Wed 04/15 10Z 0.23 2813  77   9  11 0.01
Wed 04/15 11Z 0.20 2710  73   8  11 0.00
Wed 04/15 12Z 0.21 2510  69   9  12 0.00
Wed 04/15 13Z 0.27 2513  70  12  11 0.00
Wed 04/15 14Z 0.29 2413  77  26  11 0.00
Wed 04/15 15Z 0.32 2314  87  50  11 0.00
Wed 04/15 16Z 0.33 2117  97  83  10 0.09
Wed 04/15 17Z 0.21 2111  96  95   9 0.04
Wed 04/15 18Z 0.25 2017  98  92  10 0.05
Wed 04/15 19Z 0.45 2122  98  87  11 0.03
Wed 04/15 20Z 0.84 2323  97  88  11 0.02
Wed 04/15 21Z 1.19 2523  96  90  11 0.04
Wed 04/15 22Z 0.72 2722  97  82  10 0.05
Wed 04/15 23Z 0.57 2820  97  76  10 0.02

Run total areal avg QPF for the Central_Greens is: 1.25 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