Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260627_0600
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)
=== ===== === ==== ==== === === === ====
Sat 06/27 06Z 0.15 3108  81  63  11 0.00
Sat 06/27 07Z 0.14 3208  81  63  11 0.00
Sat 06/27 08Z 0.12 3208  82  66  11 0.00
Sat 06/27 09Z 0.09 3207  81  69  11 0.00
Sat 06/27 10Z 0.08 3105  80  72  11 0.00
Sat 06/27 11Z 0.08 3105  80  76  11 0.00
Sat 06/27 12Z 0.08 3104  81  77  11 0.00
Sat 06/27 13Z 0.07 3104  82  73  11 0.00
Sat 06/27 14Z 0.05 3203  82  67  11 0.00
Sat 06/27 15Z 0.05 3002  85  64  11 0.00
Sat 06/27 16Z 0.05 3001  87  62  11 0.00
Sat 06/27 17Z 0.05 3101  88  58  11 0.02
Sat 06/27 18Z 0.05 3201  87  55  11 0.03
Sat 06/27 19Z 0.06 3201  87  50  12 0.02
Sat 06/27 20Z 0.10 3202  86  50  12 0.03
Sat 06/27 21Z 0.07 3302  86  46  12 0.04
Sat 06/27 22Z 0.04 3502  86  44  12 0.01
Sat 06/27 23Z 0.07 0103  86  50  12 0.01
Sun 06/28 00Z 0.08 0202  86  47  12 0.01
Sun 06/28 01Z 0.09 0402  85  47  12 0.01
Sun 06/28 02Z 0.11 0502  85  48  12 0.00
Sun 06/28 03Z 0.08 0402  85  49  12 0.00
Sun 06/28 04Z 0.07 0302  86  51  12 0.00
Sun 06/28 05Z 0.08 0203  87  53  11 0.00
Sun 06/28 06Z 0.05 0103  86  55  11 0.00
Sun 06/28 07Z 0.03 0003  84  55  11 0.00
Sun 06/28 08Z 0.03 3505  79  45  11 0.00
Sun 06/28 09Z 0.03 3505  76  35  11 0.00
Sun 06/28 10Z 0.02 3506  73  26  11 0.00
Sun 06/28 11Z 0.04 3507  71  25  11 0.00
Sun 06/28 12Z 0.07 0007  70  27  11 0.00
Sun 06/28 13Z 0.07 0106  70  26  11 0.00
Sun 06/28 14Z 0.10 0105  71  25  11 0.00
Sun 06/28 15Z 0.12 0204  73  21  11 0.00
Sun 06/28 16Z 0.14 0103  76  19  11 0.00
Sun 06/28 17Z 0.13 0003  78  15  11 0.00
Sun 06/28 18Z 0.08 3503  79  12  12 0.00
Sun 06/28 19Z 0.09 3504  79  13  12 0.01
Sun 06/28 20Z 0.08 3404  79  12  12 0.00
Sun 06/28 21Z 0.07 3404  80   8  12 0.00
Sun 06/28 22Z 0.05 3404  79   6  12 0.00
Sun 06/28 23Z 0.04 3405  78   8  12 0.00
Mon 06/29 00Z 0.11 0007  78   8  12 0.00
Mon 06/29 01Z 0.16 0009  79  12  12 0.01
Mon 06/29 02Z 0.23 0209  78   9  12 0.01
Mon 06/29 03Z 0.23 0209  76   7  12 0.00
Mon 06/29 04Z 0.25 0309  74   7  12 0.00
Mon 06/29 05Z 0.21 0407  75   8  12 0.00
Mon 06/29 06Z 0.11 0304  72  10  12 0.00
Mon 06/29 07Z 0.03 0004  70  12  12 0.00
Mon 06/29 08Z 0.03 3405  69  14  12 0.00
Mon 06/29 09Z 0.03 3406  67  16  12 0.00
Mon 06/29 10Z 0.03 3507  63  16  12 0.00
Mon 06/29 11Z 0.04 3508  61  15  12 0.00
Mon 06/29 12Z 0.08 0008  60  15  12 0.00
Mon 06/29 13Z 0.12 0107  60  14  12 0.00
Mon 06/29 14Z 0.12 0106  63  15  12 0.00
Mon 06/29 15Z 0.16 0105  68  16  12 0.00
Mon 06/29 16Z 0.13 0002  71  16  12 0.00
Mon 06/29 17Z 0.20 0301  70  14  12 0.00

Run total areal avg QPF for the Central_Greens is: 0.21 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