Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260803_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 08/03 12Z 0.20 1817  97  93  15 0.00
Mon 08/03 13Z 0.26 1917  99  88  15 0.02
Mon 08/03 14Z 0.36 2018  99  76  15 0.01
Mon 08/03 15Z 0.46 2018  98  72  15 0.01
Mon 08/03 16Z 0.44 1918  98  64  16 0.01
Mon 08/03 17Z 0.51 2019  96  75  16 0.02
Mon 08/03 18Z 0.51 2118  97  93  16 0.21
Mon 08/03 19Z 0.77 2320  94  78  15 0.26
Mon 08/03 20Z 0.93 2420  92  35  14 0.00
Mon 08/03 21Z 1.26 2522  92  53  13 0.01
Mon 08/03 22Z 0.88 2623  97  75  13 0.03
Mon 08/03 23Z 0.77 2928  98  85  12 0.10
Tue 08/04 00Z 0.75 3032  98  95  10 0.11
Tue 08/04 01Z 0.63 3133  94  70  10 0.04
Tue 08/04 02Z 0.71 3134  88  19  10 0.00
Tue 08/04 03Z 0.56 3231  81   8  10 0.00
Tue 08/04 04Z 0.55 3229  81  10  10 0.00
Tue 08/04 05Z 0.66 3126  88   5  10 0.00
Tue 08/04 06Z 0.71 3026  87   4  10 0.00
Tue 08/04 07Z 0.69 3024  82   4  10 0.00
Tue 08/04 08Z 0.65 3022  78   5  11 0.00
Tue 08/04 09Z 0.61 3022  71   3  11 0.00
Tue 08/04 10Z 0.56 3023  63   3  12 0.00
Tue 08/04 11Z 0.52 3022  57   2  12 0.00
Tue 08/04 12Z 0.49 3021  54   1  13 0.00
Tue 08/04 13Z 0.45 3021  52   1  13 0.00
Tue 08/04 14Z 0.40 3019  50   2  14 0.00
Tue 08/04 15Z 0.36 3016  46   2  14 0.00
Tue 08/04 16Z 0.32 3014  44   1  14 0.00
Tue 08/04 17Z 0.30 2911  46   1  15 0.00
Tue 08/04 18Z 0.30 2809  50   1  15 0.00
Tue 08/04 19Z 0.28 2807  50   2  15 0.00
Tue 08/04 20Z 0.27 2707  51   3  15 0.00
Tue 08/04 21Z 0.24 2606  52   4  16 0.00
Tue 08/04 22Z 0.19 2605  53   5  16 0.00
Tue 08/04 23Z 0.15 2504  52   6  16 0.00
Wed 08/05 00Z 0.12 2204  50   7  16 0.00
Wed 08/05 01Z 0.17 2207  48   9  16 0.00
Wed 08/05 02Z 0.21 2208  43  11  17 0.00
Wed 08/05 03Z 0.19 2209  39  12  17 0.00
Wed 08/05 04Z 0.21 2309  37  12  17 0.00
Wed 08/05 05Z 0.22 2309  36  11  18 0.00
Wed 08/05 06Z 0.21 2409  35   8  18 0.00
Wed 08/05 07Z 0.22 2409  37   4  17 0.00
Wed 08/05 08Z 0.22 2509  41   2  17 0.00
Wed 08/05 09Z 0.22 2509  43   1  17 0.00
Wed 08/05 10Z 0.21 2508  44   2  16 0.00
Wed 08/05 11Z 0.21 2508  46   2  16 0.00
Wed 08/05 12Z 0.22 2408  46   1  16 0.00
Wed 08/05 13Z 0.25 2409  47   1  16 0.00
Wed 08/05 14Z 0.26 2409  46   1  16 0.00
Wed 08/05 15Z 0.29 2409  51   1  15 0.00
Wed 08/05 16Z 0.27 2308  54   2  15 0.00
Wed 08/05 17Z 0.24 2208  50   4  16 0.00
Wed 08/05 18Z 0.27 2210  49  10  16 0.00
Wed 08/05 19Z 0.30 2211  51  15  16 0.00
Wed 08/05 20Z 0.32 2112  53  30  16 0.00
Wed 08/05 21Z 0.32 2112  50  38  17 0.00
Wed 08/05 22Z 0.34 2212  45  41  17 0.00
Wed 08/05 23Z 0.36 2213  45  37  17 0.00

Run total areal avg QPF for the Central_Greens is: 0.83 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