NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260817_1800
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 08/17 18Z 0.27 2606  96  81  14 0.00
Mon 08/17 19Z 0.14 2603  93  75  15 0.00
Mon 08/17 20Z 0.10 2502  92  77  16 0.00
Mon 08/17 21Z 0.13 2702  93  79  15 0.02
Mon 08/17 22Z 0.16 3003  94  83  15 0.05
Mon 08/17 23Z 0.13 3304  95  84  15 0.10
Tue 08/18 00Z 0.15 0104  96  87  14 0.01
Tue 08/18 01Z 0.12 0104  93  88  15 0.04
Tue 08/18 02Z 0.15 0204  93  94  15 0.20
Tue 08/18 03Z 0.14 0404  93  95  15 0.11
Tue 08/18 04Z 0.12 0703  94  88  15 0.01
Tue 08/18 05Z 0.08 0401  95  81  14 0.01
Tue 08/18 06Z 0.05 0002  96  66  14 0.01
Tue 08/18 07Z 0.04 3504  96  53  14 0.01
Tue 08/18 08Z 0.03 3505  94  42  14 0.01
Tue 08/18 09Z 0.02 3506  93  31  14 0.01
Tue 08/18 10Z 0.02 3506  90  26  14 0.00
Tue 08/18 11Z 0.02 3406  88  17  14 0.00
Tue 08/18 12Z 0.02 3505  88  14  13 0.00
Tue 08/18 13Z 0.02 3505  89   8  13 0.00
Tue 08/18 14Z 0.03 3503  90   6  13 0.00
Tue 08/18 15Z 0.03 3502  91   5  13 0.00
Tue 08/18 16Z 0.04 3302  92   4  13 0.01
Tue 08/18 17Z 0.06 3102  91   3  13 0.01
Tue 08/18 18Z 0.11 3004  91   3  13 0.01
Tue 08/18 19Z 0.11 3004  88   3  13 0.00
Tue 08/18 20Z 0.16 2905  86   3  13 0.00
Tue 08/18 21Z 0.22 2907  84   4  13 0.00
Tue 08/18 22Z 0.12 3004  80   3  13 0.00
Tue 08/18 23Z 0.10 2903  80   3  13 0.00
Wed 08/19 00Z 0.15 2804  82   9  13 0.00
Wed 08/19 01Z 0.13 2804  82   8  12 0.00
Wed 08/19 02Z 0.16 2804  83  15  12 0.00
Wed 08/19 03Z 0.13 2804  84  11  12 0.00
Wed 08/19 04Z 0.14 2704  87   6  12 0.00
Wed 08/19 05Z 0.20 2806  91   6  11 0.00
Wed 08/19 06Z 0.14 2804  90  12  11 0.00
Wed 08/19 07Z 0.15 2804  90  15  11 0.00
Wed 08/19 08Z 0.15 2805  90  11  11 0.00
Wed 08/19 09Z 0.13 2804  88  15  11 0.00
Wed 08/19 10Z 0.17 2706  87  12  11 0.00
Wed 08/19 11Z 0.18 2706  82  10  12 0.00
Wed 08/19 12Z 0.17 2607  75  25  12 0.00
Wed 08/19 13Z 0.21 2608  70  47  13 0.00
Wed 08/19 14Z 0.22 2509  67  59  13 0.00
Wed 08/19 15Z 0.24 2509  65  69  13 0.00
Wed 08/19 16Z 0.26 2409  60  65  13 0.00
Wed 08/19 17Z 0.34 2411  57  61  13 0.00
Wed 08/19 18Z 0.45 2414  52  51  14 0.00
Wed 08/19 19Z 0.55 2416  54  45  15 0.00
Wed 08/19 20Z 0.62 2516  71  48  14 0.00
Wed 08/19 21Z 0.83 2517  84  38  14 0.00
Wed 08/19 22Z 0.75 2518  91  29  13 0.00
Wed 08/19 23Z 0.69 2518  92  29  13 0.01
Thu 08/20 00Z 0.79 2520  91  32  13 0.01
Thu 08/20 01Z 0.79 2520  92  28  13 0.01
Thu 08/20 02Z 0.65 2618  90  31  14 0.01
Thu 08/20 03Z 0.57 2618  87  34  14 0.02
Thu 08/20 04Z 0.50 2617  84  29  14 0.01
Thu 08/20 05Z 0.41 2715  80  25  14 0.01

Run total areal avg QPF for the Central_Greens is: 0.70 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