Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260630_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 06/30 00Z 0.16 3307  52   9  15 0.00
Tue 06/30 01Z 0.14 3307  48   8  15 0.00
Tue 06/30 02Z 0.07 3405  45   7  15 0.00
Tue 06/30 03Z 0.06 3403  45   8  14 0.00
Tue 06/30 04Z 0.06 3000  44  10  14 0.00
Tue 06/30 05Z 0.16 2502  42  10  14 0.00
Tue 06/30 06Z 0.43 2806  42  10  14 0.00
Tue 06/30 07Z 0.83 2806  51  13  14 0.00
Tue 06/30 08Z 0.70 2706  61  15  14 0.00
Tue 06/30 09Z 0.45 2507  66  24  14 0.00
Tue 06/30 10Z 0.38 2607  67  26  14 0.00
Tue 06/30 11Z 0.38 2607  68  30  14 0.00
Tue 06/30 12Z 0.33 2407  69  41  14 0.00
Tue 06/30 13Z 0.38 2307  67  46  14 0.00
Tue 06/30 14Z 0.60 2307  67  48  14 0.00
Tue 06/30 15Z 1.39 2307  66  50  14 0.00
Tue 06/30 16Z 1.04 2209  63  69  15 0.00
Tue 06/30 17Z 0.87 2211  60  71  15 0.00
Tue 06/30 18Z 1.62 2211  60  83  15 0.00
Tue 06/30 19Z 0.80 2009  59  82  15 0.00
Tue 06/30 20Z 1.00 2010  60  89  16 0.00
Tue 06/30 21Z 0.64 2009  58  87  16 0.00
Tue 06/30 22Z 0.51 2011  59  90  16 0.00
Tue 06/30 23Z 0.49 2014  69  86  16 0.00
Wed 07/01 00Z 0.53 2016  73  94  16 0.00
Wed 07/01 01Z 0.55 2117  79  88  17 0.00
Wed 07/01 02Z 0.60 2218  82  87  17 0.00
Wed 07/01 03Z 0.63 2221  96  90  17 0.03
Wed 07/01 04Z 0.61 2420  97  71  17 0.07
Wed 07/01 05Z 0.59 2518  96  57  17 0.02
Wed 07/01 06Z 0.60 2618  96  50  17 0.01
Wed 07/01 07Z 0.56 2618  97  48  17 0.06
Wed 07/01 08Z 0.48 2515  97  37  18 0.06
Wed 07/01 09Z 0.44 2515  94  29  18 0.02
Wed 07/01 10Z 0.42 2515  93  25  18 0.01
Wed 07/01 11Z 0.47 2517  94  32  18 0.01
Wed 07/01 12Z 0.56 2520  95  15  18 0.02
Wed 07/01 13Z 0.58 2620  96  32  18 0.02
Wed 07/01 14Z 0.59 2719  96  54  18 0.01
Wed 07/01 15Z 0.49 2717  89  50  19 0.00
Wed 07/01 16Z 0.44 2816  78  58  20 0.00
Wed 07/01 17Z 0.41 2814  79  57  20 0.00
Wed 07/01 18Z 0.42 2813  85  54  20 0.00
Wed 07/01 19Z 0.40 2812  86  48  20 0.00
Wed 07/01 20Z 0.35 2811  80  33  21 0.00
Wed 07/01 21Z 0.39 2712  78  25  21 0.00
Wed 07/01 22Z 0.38 2612  72  19  22 0.00
Wed 07/01 23Z 0.38 2612  64  17  23 0.00
Thu 07/02 00Z 0.44 2615  61  20  23 0.00
Thu 07/02 01Z 0.61 2621  64  25  22 0.00
Thu 07/02 02Z 0.77 2624  68  33  22 0.00
Thu 07/02 03Z 0.62 2622  74  42  22 0.00
Thu 07/02 04Z 0.70 2526  86  44  21 0.00
Thu 07/02 05Z 0.67 2725  82  50  22 0.00
Thu 07/02 06Z 0.54 2824  67  51  22 0.00
Thu 07/02 07Z 0.49 2923  68  53  21 0.00
Thu 07/02 08Z 0.41 3021  74  57  20 0.00
Thu 07/02 09Z 0.38 3021  79  45  20 0.00
Thu 07/02 10Z 0.38 2920  75  51  20 0.00
Thu 07/02 11Z 0.37 2920  71  40  21 0.00

Run total areal avg QPF for the Central_Greens is: 0.34 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