Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260626_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)
=== ===== === ==== ==== === === === ====
Fri 06/26 00Z 0.55 2312  77  95  10 0.00
Fri 06/26 01Z 0.36 2111  72  97  10 0.01
Fri 06/26 02Z 0.29 1913  70  98  10 0.01
Fri 06/26 03Z 0.17 1714  83  98  10 0.02
Fri 06/26 04Z 0.10 1617  91  99  10 0.03
Fri 06/26 05Z 0.07 1621  96  97  10 0.07
Fri 06/26 06Z 0.11 1724  96  96  10 0.14
Fri 06/26 07Z 0.13 1726  94  96  10 0.10
Fri 06/26 08Z 0.10 1724  88  92  10 0.01
Fri 06/26 09Z 0.17 1824  90  90  10 0.00
Fri 06/26 10Z 0.16 1821  93  87  10 0.00
Fri 06/26 11Z 0.26 2017  94  83  10 0.01
Fri 06/26 12Z 0.30 2017  95  64  10 0.00
Fri 06/26 13Z 0.31 2016  94  66  10 0.01
Fri 06/26 14Z 0.33 2114  96  61  10 0.01
Fri 06/26 15Z 0.36 2213  97  67  11 0.00
Fri 06/26 16Z 0.41 2213  99  58  11 0.01
Fri 06/26 17Z 0.49 2313  97  47  11 0.00
Fri 06/26 18Z 0.57 2311  94  42  11 0.00
Fri 06/26 19Z 0.74 2211  92  54  11 0.00
Fri 06/26 20Z 1.29 2211  94  78  12 0.15
Fri 06/26 21Z 0.98 2614  93  79  12 0.28
Fri 06/26 22Z 0.49 3018  90  84  11 0.17
Fri 06/26 23Z 0.26 3216  85  64  11 0.04
Sat 06/27 00Z 0.32 3112  87  63  11 0.00
Sat 06/27 01Z 0.38 2913  92  48  11 0.00
Sat 06/27 02Z 0.36 2912  93  43  11 0.00
Sat 06/27 03Z 0.34 2913  94  44  11 0.01
Sat 06/27 04Z 0.28 3011  94  38  11 0.01
Sat 06/27 05Z 0.27 3012  94  38  10 0.01
Sat 06/27 06Z 0.20 3111  93  44  10 0.01
Sat 06/27 07Z 0.14 3211  91  54  10 0.01
Sat 06/27 08Z 0.11 3210  88  56  10 0.00
Sat 06/27 09Z 0.11 3209  84  58  10 0.00
Sat 06/27 10Z 0.10 3209  81  54  11 0.00
Sat 06/27 11Z 0.08 3310  80  48  11 0.00
Sat 06/27 12Z 0.06 3310  81  45  11 0.00
Sat 06/27 13Z 0.07 3310  83  45  10 0.00
Sat 06/27 14Z 0.08 3309  86  43  10 0.00
Sat 06/27 15Z 0.08 3307  89  43  10 0.00
Sat 06/27 16Z 0.13 3305  89  41  10 0.00
Sat 06/27 17Z 0.26 3203  89  40  11 0.00
Sat 06/27 18Z 0.28 3103  87  45  11 0.02
Sat 06/27 19Z 0.35 3103  85  47  11 0.02
Sat 06/27 20Z 0.36 3103  84  45  11 0.01
Sat 06/27 21Z 0.11 3302  83  44  12 0.01
Sat 06/27 22Z 0.06 3201  85  51  12 0.01
Sat 06/27 23Z 0.07 3202  85  61  12 0.01
Sun 06/28 00Z 0.03 3402  84  62  12 0.02
Sun 06/28 01Z 0.03 3502  83  64  12 0.01
Sun 06/28 02Z 0.02 3402  82  65  12 0.00
Sun 06/28 03Z 0.02 3402  80  64  12 0.00
Sun 06/28 04Z 0.04 0002  80  62  11 0.00
Sun 06/28 05Z 0.02 3502  81  58  11 0.00
Sun 06/28 06Z 0.02 0002  81  55  11 0.00
Sun 06/28 07Z 0.02 3402  81  53  11 0.00
Sun 06/28 08Z 0.03 3303  80  49  11 0.00
Sun 06/28 09Z 0.03 3404  79  45  11 0.00
Sun 06/28 10Z 0.02 3505  79  39  11 0.00
Sun 06/28 11Z 0.02 3506  78  40  11 0.00

Run total areal avg QPF for the Central_Greens is: 1.23 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