Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260623_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 06/23 00Z 0.28 1416  93  99   8 0.00
Tue 06/23 01Z 0.29 1421  94  99   9 0.03
Tue 06/23 02Z 0.15 1520  96  93  10 0.03
Tue 06/23 03Z 0.05 1620  97  95  10 0.02
Tue 06/23 04Z 0.07 1719  98  98  11 0.03
Tue 06/23 05Z 0.11 1815  99  99  11 0.03
Tue 06/23 06Z 0.10 1910  99  98  11 0.03
Tue 06/23 07Z 0.07 1907  99  96  11 0.03
Tue 06/23 08Z 0.05 1804  99  95  11 0.03
Tue 06/23 09Z 0.05 1902  99  92  10 0.03
Tue 06/23 10Z 0.04 2801  99  86  10 0.01
Tue 06/23 11Z 0.05 3204  99  79  10 0.01
Tue 06/23 12Z 0.04 3407  99  70  10 0.00
Tue 06/23 13Z 0.04 3409  97  60  10 0.00
Tue 06/23 14Z 0.03 3409  95  40  10 0.00
Tue 06/23 15Z 0.03 3410  93  24  10 0.00
Tue 06/23 16Z 0.04 3411  90  15  10 0.00
Tue 06/23 17Z 0.04 3412  88  12  10 0.00
Tue 06/23 18Z 0.08 3412  86   8  10 0.00
Tue 06/23 19Z 0.11 3412  86   6  10 0.00
Tue 06/23 20Z 0.17 3312  86   6  10 0.00
Tue 06/23 21Z 0.15 3313  85   5  10 0.00
Tue 06/23 22Z 0.20 3314  86   6  10 0.00
Tue 06/23 23Z 0.18 3315  89   5  10 0.00
Wed 06/24 00Z 0.21 3318  93   7  10 0.00
Wed 06/24 01Z 0.24 3319  91  11  10 0.01
Wed 06/24 02Z 0.21 3318  88  10  10 0.01
Wed 06/24 03Z 0.15 3319  85  12  10 0.01
Wed 06/24 04Z 0.14 3321  90  15  10 0.01
Wed 06/24 05Z 0.10 3421  94  20   9 0.00
Wed 06/24 06Z 0.07 3420  94  22   9 0.00
Wed 06/24 07Z 0.06 3418  93  21   9 0.00
Wed 06/24 08Z 0.07 3417  91  21   9 0.00
Wed 06/24 09Z 0.14 3317  89  24   9 0.00
Wed 06/24 10Z 0.21 3217  87  27   9 0.00
Wed 06/24 11Z 0.29 3118  85  28   8 0.00
Wed 06/24 12Z 0.34 3118  87  30   8 0.00
Wed 06/24 13Z 0.38 3118  87  30   8 0.00
Wed 06/24 14Z 0.55 3118  86  34   7 0.00
Wed 06/24 15Z 1.06 3017  86  34   7 0.00
Wed 06/24 16Z 3.32 2915  86  37   8 0.00
Wed 06/24 17Z 5.10 2815  88  48   8 0.00
Wed 06/24 18Z 5.34 2815  86  44   8 0.00
Wed 06/24 19Z 5.87 2815  85  43   9 0.00
Wed 06/24 20Z 4.00 2816  85  40   9 0.00
Wed 06/24 21Z 3.35 2917  85  40   9 0.00
Wed 06/24 22Z 2.62 3018  83  41   9 0.00
Wed 06/24 23Z 1.31 3018  83  38   9 0.00
Thu 06/25 00Z 0.95 3019  83  39   9 0.00
Thu 06/25 01Z 1.12 3018  84  36   9 0.00
Thu 06/25 02Z 0.97 3018  88  36   9 0.00
Thu 06/25 03Z 0.84 3019  87  35   9 0.00
Thu 06/25 04Z 0.67 3019  84  38   9 0.00
Thu 06/25 05Z 0.49 3118  82  38   9 0.00
Thu 06/25 06Z 0.36 3217  79  38  10 0.00
Thu 06/25 07Z 0.31 3215  78  40  10 0.00
Thu 06/25 08Z 0.21 3313  77  39  10 0.00
Thu 06/25 09Z 0.17 3311  77  40  10 0.00
Thu 06/25 10Z 0.12 3307  76  39  10 0.00
Thu 06/25 11Z 0.10 3305  76  39  10 0.00

Run total areal avg QPF for the Central_Greens is: 0.32 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